Flatland

Flatland maps between rich, structured Python application data and the string-oriented flat namespace of web forms, key/value stores, text files and user input. Flatland provides a schema-driven mapping toolkit with optional data validation.

Flatland is great for:

• Collecting, validating, re-displaying and processing HTML form data
• Dealing with rich structures (lists, dicts, lists of dicts, etc.) in web data
• Validating JSON, YAML, and other structured formats
• Associating arbitrary Python types with JSON, .ini, or sys.argv members that would otherwise deserialize as simple strings.
• Reusing a single data schema for HTML, JSON APIs, RPC, …

The core of the Flatland toolkit is a flexible and extensible declarative schema system representing many data types and structures.

A validation system and library of schema-aware validators is also provided, with rich i18n capabilities for use in HTML, network APIs and other environments where user-facing messaging is required.

Contents

Overview

Philosophy

flatland’s design stems from a few basic tenets:

• All input is suspect
• Input can come from multiple sources and interfaces
• Bad input isn’t exceptional: it is expected

With flatland, you describe exactly what elements your form may contain. Forms extract and process only their known elements out of the (key, value) input data. Unexpected or malicious data will not be processed.

The description of forms and their fields is data-centric rather than HTML or interface-centric. In a flatland form schema, a password input field is simply a string, not a “PasswordInput” or the like. The decision about how to represent that field is left up to another layer entirely. Maybe you do want an <input type="password"> control, or maybe <input type="hidden"> in some cases, or sometimes the data is coming in as JSON. flatland can act as another type of M in your M/VC, MC, MVC or MTV.

Humans are imperfect and filling out forms will always be error-prone. flatland recognizes this and provides features to make error detection and correction part of the regular workflow of a form. By default, validation routines will consider every element of a form and mark all problematic fields, allowing users to take action on all issues at once.

Introduction

Field schemas define all possible fields the form may contain. A schema may a single field, a collection of fields, or an even richer structure. Nested mappings and lists of fields are supported, as well as compound fields and even more exotic types.

from flatland import Form, String

class SignInForm(Form):
    username = String
    password = String

Field schemas are long-lived objects similar to class definitions. The instantiations of a flatland schema are called data elements, a tree structure of data-holding objects. The elements of a flatland form may be initiated blank, using default values, or with values taken from your objects.

form = SignInForm.from_flat(request.POST)
if form.validate():
    logging.info(u"sign-in: %s" % form['username'].value)
    redirect('/app/')
else:
    render('login.html', form=form)

Elements are rich objects that validate and normalize input data as well as hold field-level error and warning messages. Elements can be exported to a native Python structure, flattened back into Unicode (key, value) pairs or used as-is in output templates for form layout, redisplay and error reporting.

>>> as_regular_python_data = form.value
>>> isinstance(as_regular_python_data, dict)
True
>>> as_regular_python_data['username']
u'jek'
>>> form2 = SignInForm(as_regular_python_data)
>>> assert form['username'].value == form2['username'].value

Defining and Using Forms

Introduction

Basic Forms

class Schema(value=Unspecified, **kw)

Bases: flatland.schema.containers.Dict

A declarative collection of named elements.

Schemas behave like Dict, but are defined with Python class syntax:

>>> from flatland import Schema, String
>>> class HelloSchema(Schema):
...     hello = String
...     world = String
...

Elements are assigned names from the attribute declaration. If a named element schema is used, a renamed copy will be assigned to the Schema to match the declaration.

>>> class HelloSchema(Schema):
...     hello = String.named('hello')    # redundant
...     world = String.named('goodbye')  # will be renamed 'world'
...
>>> helloworld = HelloSchema()
>>> sorted(helloworld.keys())
[u'hello', u'world']

Schemas may embed other container fields and other schemas:

>>> from flatland import List
>>> class BigSchema(Schema):
...     main_hello = HelloSchema
...     alt_hello = List.of(String.named('alt_name'),
...                         HelloSchema.named('alt_hello'))
...

This would create a Schema with one HelloSchema embedded as main_hello, and a list of zero or more dicts, each containing an alt_name and another HelloSchema named alt_hello.

Schemas may inherit from other Schemas or Dicts. Element attributes declared in a subclass will override those of a superclass. Multiple inheritance is supported.

The special behavior of Schema is limited to class construction time only. After construction, the Schema acts exactly like a Dict. In particular, fields declared as class attributes as above do not remain class attributes. They are removed from the class dictionary and placed in the field_schema:

>>> hasattr(HelloSchema, 'hello')
False
>>> sorted([field.name for field in HelloSchema.field_schema])
[u'hello', u'world']

The order of field_schema is undefined.

class SparseSchema(value=Unspecified, **kw)

Bases: flatland.schema.containers.SparseDict

A sparse variant of Schema.

Exactly as Schema, but based upon ~flatland.schema.containers.SparseDict`.

class Form(value=Unspecified, **kw)

Bases: flatland.schema.containers.Dict

An alias for Schema, for older flatland version compatibility.

Elements

Elements describe the possible fields of a form; their names, structure, Python types and rules for validation. A typical schema consists of at least one container type and one or more scalar types:

from flatland import Dict, String
SearchSchema = Dict.named('search').of(String.named(u'keywords'))

Todo

FIXME UPDATE:

FieldSchemas are a bit like Python class definitions: they need be defined only once and don’t do much on their own. FieldSchema.create_element() produces Elements; closely related objects that hold and manipulate form data. Much like a Python class, a single FieldSchema may produce an unlimited number of Element instances.

>>> form = SearchSchema({u'keywords': u'foo bar baz'})
>>> form.value
{u'keywords': u'foo bar baz'}

Todo

FIXME UPDATE:

FieldSchema instances may be freely composed and shared among many containers.

>>> from flatland import List
>>> ComposedSchema = Dict.of(SearchSchema,
...                          List.named(u'many_searches').of(SearchSchema))
>>> form = ComposedSchema()
>>> sorted(form.value.keys())
[u'many_searches', u'search']

Todo

FIXME UPDATE:

Elements can be supplied to template environments and used to great effect there: elements contain all of the information needed to display or redisplay a HTML form field, including errors specific to a field.

The u, x, xa and el() members are especially useful in templates and have shortened names to help preserve your sanity when used in markup.

Element

class Element(value=Unspecified, **kw)

Base class for form fields.

A data node that stores a Python and a text value plus added state.

Instance Attributes

parent

An owning element, or None if element is topmost or not a member of a hierarchy.

valid

errors

A list of validation error messages.

warnings

A list of validation warning messages.

Members

name = None

The string name of the element.

optional = False

If True, validate() will return True when no value has been set.

validators are not called for optional, empty elements.

validators = ()

A sequence of validators, invoked by validate().

See Validation.

default = None

The default value of this element.

default_factory = None

A callable to generate default element values. Passed an element.

default_factory will be used preferentially over default.

ugettext = None

If set, provides translation support to validation messages.

See Message Internationalization.

ungettext = None

If set, provides translation support to validation messages.

See Message Internationalization.

value = None

The element’s native Python value.

Only validation routines should write this attribute directly: use set() to update the element’s value.

raw = Unset

The element’s raw, unadapted value from input.

u = u''

A string representation of the element’s value.

As in value, writing directly to this attribute should be restricted to validation routines.

properties = {}

A mapping of arbitrary data associated with the element.

named(name)

Return a class with name = name

Parameters:name – a string or None. Returns:a new class

using(**overrides)

Return a class with attributes set from **overrides.

Parameters:**overrides – new values for any attributes already present on the class. A TypeError is raised for unknown attributes. Returns:a new class

validated_by(*validators)

Return a class with validators set to *validators.

Parameters:*validators – one or more validator functions, replacing any validators present on the class. Returns:a new class

including_validators(*validators, **kw)

Return a class with additional *validators.

Parameters:

• *validators – one or more validator functions
• position – defaults to -1. By default, additional validators are placed after existing validators. Use 0 for before, or any other list index to splice in validators at that point.

Returns:

a new class

with_properties(*iterable, **properties)

Return a class with **properties set.

Param:optional positional parameter, an iterable of property name / value pairs Parameters:**properties – property names and values as keyword arguments Returns:a new class

classmethod from_flat(pairs, **kw)

Return a new element with its value initialized from pairs.

Parameters:**kw – passed through to the element_type.

This is a convenience constructor for:

element = cls(**kw)
element.set_flat(pairs)

classmethod from_defaults(**kw)

Return a new element with its value initialized from field defaults.

Parameters:**kw – passed through to the element_type.

This is a convenience constructor for:

element = cls(**kw)
element.set_default()

all_valid

True if this element and all children are valid.

root

The top-most parent of the element.

parents

An iterator of all parent elements.

path

An iterator of all elements from root to the Element, inclusive.

children

An iterator of immediate child elements.

all_children

An iterator of all child elements, breadth-first.

fq_name()

Return the fully qualified path name of the element.

Returns find() compatible element path string from the Element.root (/) down to the element.

>>> from flatland import Dict, Integer
>>> Point = Dict.named(u'point').of(Integer.named(u'x'),
...                                 Integer.named(u'y'))
>>> p = Point(dict(x=10, y=20))
>>> p.name
u'point'
>>> p.fq_name()
u'/'
>>> p['x'].name
u'x'
>>> p['x'].fq_name()
u'/x'

The index used in a path may not be the name of the element. For example, sequence members are referenced by their numeric index.

>>> from flatland import List, String
>>> Addresses = List.named('addresses').of(String.named('address'))
>>> form = Addresses([u'uptown', u'downtown'])
>>> form.name
u'addresses'
>>> form.fq_name()
u'/'
>>> form[0].name
u'address'
>>> form[0].fq_name()
u'/0'

find(path, single=False, strict=True)

Find child elements by string path.

Parameters:

• path – a /-separated string specifying elements to select, such as ‘child/grandchild/great grandchild’. Relative & absolute paths are supported, as well as container expansion. See Path Lookups.
• single – if true, return a scalar result rather than a list of elements. If no elements match path, None is returned. If multiple elements match, a LookupError is raised. If multiple elements are found and strict is false, an unspecified element from the result set is returned.
• strict – defaults to True. If path specifies children or sequence indexes that do not exist, a LookupError is raised.

Returns:

a list of Element instances, an Element if single is true, or raises LookupError.

>>> cities = form.find('/contact/addresses[:]/city')
>>> [el.value for el in cities]
[u'Kingsport', u'Dunwich']
>>> form.find('/contact/name', single=True)
<String u'name'; value=u'Obed Marsh'>

find_one(path)

Find a single element at path.

An alias for find(). Equivalent to find(path, single=True, strict=True).

add_error(message)

Register an error message on this element, ignoring duplicates.

add_warning(message)

Register a warning message on this element, ignoring duplicates.

flattened_name(sep=u'_')

Return the element’s complete flattened name as a string.

Joins this element’s path with sep and returns the fully qualified, flattened name. Encodes all Container and other structures into a single string.

Example:

>>> import flatland
>>> form = flatland.List('addresses',
...                      flatland.String('address'))
>>> element = form()
>>> element.set([u'uptown', u'downtown'])
>>> element[0].value
u'uptown'
>>> element['0'].flattened_name()
u'addresses_0_address'

flatten(sep=u'_', value=<operator.attrgetter object>)

Export an element hierarchy as a flat sequence of key, value pairs.

Parameters:

• sep – a string, will join together element names.
• value – a 1-arg callable called once for each element. Defaults to a callable that returns the u of each element.

Encodes the element hierarchy in a sep-separated name string, paired with any representation of the element you like. The default is the text value of the element, and the output of the default flatten() can be round-tripped with set_flat().

Given a simple form with a string field and a nested dictionary:

>>> from flatland import Schema, Dict, String
>>> class Nested(Schema):
...     contact = Dict.of(String.named(u'name'),
...                       Dict.named(u'address').
...                            of(String.named(u'email')))
...
>>> element = Nested()
>>> element.flatten()
[(u'contact_name', u''), (u'contact_address_email', u'')]

The value of each pair can be customized with the value callable:

>>> element.flatten(value=operator.attrgetter('u'))
[(u'contact_name', u''), (u'contact_address_email', u'')]
>>> element.flatten(value=lambda el: el.value)
[(u'contact_name', None), (u'contact_address_email', None)]

Solo elements will return a sequence containing a single pair:

>>> element['name'].flatten()
[(u'contact_name', u'')]

set(obj)

Process obj and assign the native and text values.

Attempts to adapt the given obj and assigns this element’s value and u attributes in tandem. Returns True if the adaptation was successful.

If adaptation succeeds, value will contain the adapted native value and u will contain a text serialized version of it. A native value of None will be represented as u’’ in u.

If adaptation fails, value will be None and u will contain str(value) (or unicode), or u'' for None.

>>> from flatland import Integer
>>> el = Integer()
>>> el.u, el.value
(u'', None)

>>> el.set('123')
True
>>> el.u, el.value
(u'123', 123)

>>> el.set(456)
True
>>> el.u, el.value
(u'456', 456)

>>> el.set('abc')
False
>>> el.u, el.value
(u'abc', None)

>>> el.set(None)
True
>>> el.u, el.value
(u'', None)

set_flat(pairs, sep=u'_')

Set element values from pairs, expanding the element tree as needed.

Given a sequence of name/value tuples or a dict, build out a structured tree of value elements.

set_default()

set() the element to the schema default.

is_empty

True if the element has no value.

validate(state=None, recurse=True)

Assess the validity of this element and its children.

Parameters:

• state – optional, will be passed unchanged to all validator callables.
• recurse – if False, do not validate children.

Returns:

True or False.

Iterates through this element and all of its children, invoking each validation on each. Each element will be visited twice: once heading down the tree, breadth-first, and again heading back up in reverse order.

Returns True if all validations pass, False if one or more fail.

default_value

A calculated “default” value.

If default_factory is present, it will be called with the element as a single positional argument. The result of the call will be returned.

Otherwise, returns default.

When comparing an element’s value to its default value, use this property in the comparison.

x

Sugar, the XML-escaped value of u.

xa

Sugar, the XML-attribute-escaped quoted value of u.

Traversal

Flatland supplies a rich set of tools for working with structured data. For this section, we’ll use the following schema as an example. It is simple yet has a bit of variety in its structure.

from flatland import Form, Dict, List, String, Integer

class Annotation(Form):
    """A spot on a 2D surface."""
    title = String
    flags = List.of(Integer)
    location = Dict.of(Integer.named('x'),
                       Integer.named('y'))

sample_data = {
  'title': 'Interesting Spot',
  'flags': [1, 3, 5],
  'location': {'x': 10, 'y': 20},
}

ann1 = Annotation(sample_data, name=u'ann1')

Going Raw

You may not even need to use any of these traversal strategies in your application. An element’s value is a full & recursive “export” of its native Python value. Many times this is sufficient.

>>> ann1['title']     # ann1 is a flatland structure
<String u'title'; value=u'Interesting Spot'>
>>> isinstance(ann1.value, dict)  # but its .value is not
True
>>> ann1.value == sample_data
True

Python Syntax

Containers elements such as Form, Dict, and List implement the Python methods you’d expect for their type. In most cases you may use them as if they were dict and list instances- the difference being that they always contain Element instances.

For example, Form and Dict can be indexed and used like dict:

>>> ann1['title'].value
u'Interesting Spot'
>>> ann1['location']['x'].value
10
>>> sorted(ann1['location'].items())
[(u'x', <Integer u'x'; value=10>), (u'y', <Integer u'y'; value=20>)]
>>> u'title' in ann1
True

And List and similar types can be used like lists:

>>> ann1['flags']
[<Integer None; value=1>, <Integer None; value=3>, <Integer None; value=5>]
>>> ann1['flags'][0].value
1
>>> ann1['flags'].value
[1, 3, 5]
>>> Integer(3) in ann1['flags']
True
>>> 3 in ann1['flags']
True

The final example is of special note: the value in the expression is not an Element. Most containers will accept native Python values in these types of expressions and convert them into a temporary Element for the operation. The example below is equivalent to the example above.

>>> ann1['flags'].member_schema(3) in ann1['flags']
True

Traversal Properties

Elements of all types support a core set of properties that allow navigation to related elements: root, parents, children, and all_children.

>>> list(ann1['flags'].children)
[<Integer None; value=1>, <Integer None; value=3>, <Integer None; value=5>]
>>> list(ann1['title'].children)  # title is a String and has no children
[]
>>> sorted(el.name for el in ann1.all_children if el.name)
[u'flags', u'location', u'title', u'x', u'y']
>>> [el.name for el in ann1['location']['x'].parents]
[u'location', u'ann1']

Each of these properties (excepting root) returns an iterator of elements.

Path Lookups

Another option for operating on elements is the find() method. find selects elements by path, a string that represents one or more related elements. Looking up elements by path is a powerful technique to use when authoring flexible & reusable validators.

>>> ann1.find('title')   # find 'ann1's child named 'title'
[<String u'title'; value=u'Interesting Spot'>]

Paths are evaluated relative to the element:

>>> ann1['location'].find('x')
[<Integer u'x'; value=10>]

Referencing parents is possible with ..:

>>> ann1['location']['x'].find('../../title')
[<String u'title'; value=u'Interesting Spot'>]

Absolute paths begin with a /.

>>> ann1['location']['x'].find('/title')
[<String u'title'; value=u'Interesting Spot'>]

Members of sequences can be selected like any other child (their index number is their name), or you can use Python-like slicing:

>>> ann1.find('/flags/0')
[<Integer None; value=1>]
>>> ann1.find('/flags[0]')
[<Integer None; value=1>]

Full Python slice notation is supported as well. With slices, paths can select more than one element.

>>> ann1.find('/flags[:]')
[<Integer None; value=1>, <Integer None; value=3>, <Integer None; value=5>]
>>> ann1.find('/flags[1:]')
[<Integer None; value=3>, <Integer None; value=5>]

Further path operations are permissible after slices. A richer schema is needed to illustrate this:

>>> Points = List.of(List.of(Dict.of(Integer.named('x'),
...                                  Integer.named('y'))))
>>> p = Points([[dict(x=1, y=1), dict(x=2, y=2)],
...             [dict(x=3, y=3)]])
>>> p.find('[:][:]/x')
[<Integer u'x'; value=1>, <Integer u'x'; value=2>, <Integer u'x'; value=3>]

The equivalent straight Python to select the same set of elements is quite a bit more wordy.

Path Syntax

/ (leading slash)

Selects the root of the element tree

element

The name of a child element

element/child

/ separates path segments

..

Traverse to the parent element

element[0]

For a sequence container element, select the 0th child

element[:]

Select all children of a container element (need not be a sequence)

element[1:5]

Select a slice of a sequence container’s children

Annotations & Properties

Flatland provides two options for annotating schemas and data.

Standard Python

Element schemas are normal Python classes and can be extended in all of the usual ways. For example, you can add an attribute when subclassing:

from flatland import String

class Textbox(String):
    tooltip = 'Undefined'

Once an attribute has been added to an element class, its value can be overridden by further subclassing or, more compactly, with the using() schema constructor:

class Password(Textbox):
    tooltip = 'Enter your password'


Password = Textbox.using(tooltip='Enter your password')
assert Password.tooltip == 'Enter your password'

Both are equivalent, and the custom tooltip will be inherited by any subclasses of Password. Likewise, instances of Password will have the attribute as well.

el = Password()
assert el.tooltip == 'Enter your password'

And because the Element() constructor allows overriding any schema attribute by keyword argument, individual element instances can be constructed with own values, masking the value provided by their class.

password_match = Textbox(tooltip='Enter your password again')

assert password_match.tooltip == 'Enter your password again'

Properties

Another option for annotation is the properties mapping of element classes and instances. Unlike class attributes, almost any object you like can be used as the key in the mapping.

The unique feature of properties is data inheritance:

from flatland import String

# Textboxes are Strings with tooltips
Textbox = String.with_properties(tooltip='Undefined')

# A Password is a Textbox with a custom tooltip message
Password = Textbox.with_properties(tooltip='Enter your password')

assert Textbox.properties['tooltip'] == 'Undefined'
assert Password.properties['tooltip'] == 'Enter your password'

Annotations made on a schema are visible to itself and any subclasses, but not to its parents.

# Add disabled to all Textboxes
Textbox.properties['disabled'] = False

# disabled is inherited from Textbox
assert Password.properties['disabled'] is False

# changes in a subclass do not affect the parent
del Password.properties['disabled']
assert 'disabled' in Textbox.properties

Annotating With Properties

To create a new schema that includes additional properties, construct it with with_properties():

Textbox = String.with_properties(tooltip='Undefined')

Or if the schema has already been created, manipulate its properties mapping:

class Textbox(String):
   pass

Textbox.properties['tooltip'] = 'Undefined'

The properties mapping is implemented as a view over the Element schema inheritance hierarchy. If annotations are added to a superclass such as String, they are visible immediately to all Strings and subclasses.

Private Annotations

To create a schema with completely unrelated properties, not inheriting from its superclass at all, declare it with using():

Alone = Textbox.using(properties={'something': 'else'})
assert 'tooltip' not in Alone.properties

Or when subclassing longhand, construct a Properties collection explicitly.

from flatland import Properties

class Alone(Textbox):
   properties = Properties(something='else')

assert 'tooltip' not in Alone.properties

An instance may also have a private collection of properties. This can be done either at or after construction:

solo1 = Textbox(properties={'something': 'else'})

solo2 = Textbox()
solo2.properties = {'something': 'else'}

Textbox.properties['background_color'] = 'red'

assert 'background_color' not in solo1.properties
assert 'background_color' not in solo2.properties

Exceptions

exception AdaptationError

Bases: exceptions.Exception

A value could not be coerced into native format.

Element Types

Strings, Numbers and Booleans

Strings

class String(value=Unspecified, **kw)

Bases: flatland.schema.scalars.Scalar

A regular old text string.

strip = True

If true, strip leading and trailing whitespace during conversion.

adapt(value)

Return a Python representation.

Returns:a text value or None

If strip is true, leading and trailing whitespace will be removed.

serialize(value)

Return a text representation.

Returns:a Unicode value or u'' if value is None

If strip is true, leading and trailing whitespace will be removed.

is_empty

True if the String is missing or has no value.

Numbers

class Integer(value=Unspecified, **kw)

Bases: flatland.schema.scalars.Number

Element type for Python’s int.

type_

alias of __builtin__.int

format = u'%i'

u'%i'

class Long(value=Unspecified, **kw)

Bases: flatland.schema.scalars.Number

Element type for Python’s long.

type_

alias of __builtin__.long

format = u'%i'

u'%i'

class Float(value=Unspecified, **kw)

Bases: flatland.schema.scalars.Number

Element type for Python’s float.

type_

alias of __builtin__.float

format = u'%f'

u'%f'

class Decimal(value=Unspecified, **kw)

Bases: flatland.schema.scalars.Number

Element type for Python’s Decimal.

type_

alias of decimal.Decimal

format = u'%f'

u'%f'

Booleans

class Boolean(value=Unspecified, **kw)

Bases: flatland.schema.scalars.Scalar

Element type for Python’s bool.

true = u'1'

The text serialization for True: u'1'.

true_synonyms = (u'on', u'true', u'True', u'1')

A sequence of acceptable string equivalents for True.

Defaults to (u'on', u'true', u'True', u'1')

false = u''

The text serialization for False: u''.

false_synonyms = (u'off', u'false', u'False', u'0', u'')

A sequence of acceptable string equivalents for False.

Defaults to (u'off', u'false', u'False', u'0', u'')

adapt(value)

Coerce value to bool.

Returns:a bool or None

If value is text, returns True if the value is in true_synonyms, False if in false_synonyms and None otherwise.

For non-text values, equivalent to bool(value).

serialize(value)

Convert bool(value) to a canonical text representation.

Returns:either self.true or self.false.

Dates and Times

class DateTime(value=Unspecified, **kw)

Bases: flatland.schema.scalars.Temporal

Element type for Python datetime.datetime.

Serializes to and from YYYY-MM-DD HH:MM:SS format.

type_

alias of datetime.datetime

class Date(value=Unspecified, **kw)

Bases: flatland.schema.scalars.Temporal

Element type for Python datetime.date.

Serializes to and from YYYY-MM-DD format.

type_

alias of datetime.date

class Time(value=Unspecified, **kw)

Bases: flatland.schema.scalars.Temporal

Element type for Python datetime.time.

Serializes to and from HH:MM:SS format.

type_

alias of datetime.time

Dicts

Todo

intro

set() Policy

Todo

strict, duck, etc.

Validation

If descent_validators is defined, these validators will be run first, before member elements are validated.

If validators is defined, these validators will be run after member elements are validated.

Dict

class Dict(value=Unspecified, **kw)

Bases: flatland.schema.containers.Mapping, dict

A mapping Container with named members.

policy = 'subset'

Deprecated. One of ‘strict’, ‘subset’ or ‘duck’. Default ‘subset’.

Operates as SetWithAllFields and SetWithKnownFields, except raises an exception immediately upon set().

To migrate to the new validators, set policy to None to disable the policy behavior.

of(*fields)

Todo

doc of()

classmethod from_object(obj, include=None, omit=None, rename=None, **kw)

Return an element initialized with an object’s attributes.

Parameters:

• obj – any object
• include – optional, an iterable of attribute names to pull from obj, if present on the object. Only these attributes will be included.
• omit – optional, an iterable of attribute names to ignore on obj. All other attributes matching a named field on the mapping will be included.
• rename – optional, a mapping of attribute-to-field name transformations. Attributes specified in the mapping will be included regardless of include or omit.
• **kw – keyword arguments will be passed to the element’s constructor.

include and omit are mutually exclusive.

This is a convenience constructor for set_by_object():

element = cls(**kw)
element.set_by_object(obj, include, omit, rename)

set(value, policy=None)

Todo

doc set()

set_by_object(obj, include=None, omit=None, rename=None)

Set fields with an object’s attributes.

Parameters:

• obj – any object
• include – optional, an iterable of attribute names to pull from obj, if present on the object. Only these attributes will be included.
• omit – optional, an iterable of attribute names to ignore on obj. All other attributes matching a named field on the mapping will be included.
• rename – optional, a mapping of attribute-to-field name transformations. Attributes specified in the mapping will be included regardless of include or omit.

include and omit are mutually exclusive.

Sets fields on self, using as many attributes as possible from obj. Object attributes that do not correspond to field names are ignored.

Mapping instances have two corresponding methods useful for round-tripping values in and out of your domain objects.

update_object() performs the inverse of set_object(), and slice() is useful for constructing new objects.

>>> user = User('biff', 'secret')
>>> form = UserForm()
>>> form.set_by_object(user)
>>> form['login'].value
u'biff'
>>> form['password'] = u'new-password'
>>> form.update_object(user, omit=['verify_password'])
>>> user.password
u'new-password'
>>> user_keywords = form.slice(omit=['verify_password'], key=str)
>>> sorted(user_keywords.keys())
['login', 'password']
>>> new_user = User(**user_keywords)

update_object(obj, include=None, omit=None, rename=None, key=<function identifier_transform>)

Update an object’s attributes using the element’s values.

Produces a slice() using include, omit, rename and key, and sets the selected attributes on obj using setattr.

Returns:nothing. obj is modified directly.

slice(include=None, omit=None, rename=None, key=None)

Return a dict containing a subset of the element’s values.

SparseDict

class SparseDict(value=Unspecified, **kw)

Bases: flatland.schema.containers.Dict

A Mapping which may contain a subset of the schema’s allowed keys.

This differs from Dict in that new instances are not created with empty values for all possible keys. In addition, mutating operations are allowed so long as the operations operate within the schema. For example, you may pop() and del members of the mapping.

minimum_fields = None

The subset of fields to autovivify on instantiation.

May be None or 'required'. If None, mappings will be created empty and mutation operations are unrestricted within the bounds of the field_schema. If required, fields with optional of False will always be present after instantiation, and attempts to remove them from the mapping with del and friends will raise TypeError.

may_contain(key)

Return True if the element schema allows a field named key.

clear() → None. Remove all items from D.

popitem() → (k, v), remove and return some (key, value) pair as a

2-tuple; but raise KeyError if D is empty.

pop(k[, d]) → v, remove specified key and return the corresponding value.

If key is not found, d is returned if given, otherwise KeyError is raised

setdefault(k[, d]) → D.get(k,d), also set D[k]=d if k not in D

set_default()

set() the element to the schema default.

Lists

Instances of List hold other elements and operate like Python lists. Lists are configured with a member_schema, such as an Integer. Each list member will be an instance of that type. The List.of() schema constructor will set member_schema:

>>> from flatland import List, Integer
>>> Numbers = List.of(Integer)
>>> Numbers.member_schema
<class 'flatland.schema.scalars.Integer'>

Python list methods and operators may be passed instances of member_schema or plain Python values. Using plain values is a shorthand for creating a member_schema instance and set()ting it with the value:

>>> ones = Numbers()
>>> ones.append(1)
>>> ones.value
[1]
>>> another_one = Integer()
>>> another_one.set(1)
True
>>> ones.append(another_one)
>>> ones.value
[1, 1]

List extends Sequence and adds positional naming to its elements. Elements are addressable via their list index in find() and their index in the list is reflected in their flattened name:

Example:

>>> from flatland import List, String
>>> Names = List.named('names').of(String.named('name'))
>>> names = Names([u'a', u'b'])
>>> names.value
[u'a', u'b']
>>> names.flatten()
[(u'names_0_name', u'a'), (u'names_1_name', u'b')]
>>> names[1].value
u'b'
>>> names.find_one('1').value
u'b'

Validation

If descent_validators is defined, these validators will be run first, before member elements are validated.

If validators is defined, these validators will be run after member elements are validated.

List

class List(value=Unspecified, **kw)

Bases: flatland.schema.containers.Sequence

An ordered, homogeneous Sequence.

slot_type

alias of ListSlot

member_schema = ()

An Element class for member elements.

See also the of() schema configuration method.

maximum_set_flat_members = 1024

Maximum list members set in a set_flat() operation.

Once this maximum of child members has been added, subsequent data will be dropped. This ceiling prevents denial of service attacks when processing Lists with prune_empty set to False; without it remote attackers can trivially exhaust memory by specifying one low and one very high index.

append(value)

Append value to end.

If value is not an instance of member_schema, it will be wrapped in a new element of that type before appending.

extend(iterable)

Append iterable values to the end.

If values of iterable are not instances of member_schema, they will be wrapped in a new element of that type before extending.

pop([index]) → item -- remove and return item at index (default last).

Raises IndexError if list is empty or index is out of range.

insert(index, value)

Insert value at index.

If value is not an instance of member_schema, it will be wrapped in a new element of that type before inserting.

remove(value)

Remove member with value value.

If value is not an instance of member_schema, it will be wrapped in a new element of that type before searching for a matching element to remove.

sort(cmp=None, key=None, reverse=False)

L.sort(cmp=None, key=None, reverse=False) – stable sort IN PLACE; cmp(x, y) -> -1, 0, 1

reverse()

L.reverse() – reverse IN PLACE

set_default()

set() the element to the schema default.

List’s set_default supports two modes for default values:

• If default is an integer, the List will be filled with that many elements. Each element will then have set_default() called on it.
• Otherwise if default has a value, the list will be set() with it.

Arrays and MultiValues

Array

class Array(value=Unspecified, **kw)

Bases: flatland.schema.containers.Sequence

A transparent homogeneous Container, for multivalued form elements.

Arrays hold a collection of values under a single name, allowing all values of a repeated (key, value) pair to be captured and used. Elements are sequence-like.

MultiValue

class MultiValue(value=Unspecified, **kw)

Bases: flatland.schema.containers.Array, flatland.schema.scalars.Scalar

A transparent homogeneous Container, for multivalued form elements.

MultiValues combine aspects of Scalar and Sequence fields, allowing all values of a repeated (key, value) pair to be captured and used.

MultiValues take on the name of their child and have no identity of their own when flattened. Elements are mostly sequence-like and can be indexed and iterated. However the u or value are scalar-like, and return values from the first element in the sequence.

u

The .u of the first item in the sequence, or u’‘.

value

The .value of the first item in the sequence, or None.

Enumerations

Constrained Types

class Constrained(value=Unspecified, **kw)

Bases: flatland.schema.scalars.Scalar

A scalar type with a constrained set of legal values.

Wraps another scalar type and ensures that a value set() is within bounds defined by valid_value(). If valid_value() returns false, the element is not converted and will have a value of None.

Constrained is a semi-abstract class that requires an implementation of valid_value(), either by subclassing or overriding on a per-instance basis through the constructor.

An example of a wrapper of int values that only allows the values of 1, 2 or 3:

>>> from flatland import Constrained, Integer
>>> def is_valid(element, value):
...     return value in (1, 2, 3)
...
>>> schema = Constrained.using(child_type=Integer, valid_value=is_valid)
>>> element = schema()
>>> element.set(u'2')
True
>>> element.value
2
>>> element.set(u'5')
False
>>> element.value is None
True

Enum is a subclass which provides a convenient enumerated wrapper.

child_type

The type of constrained value, defaulting to String.

alias of String

static valid_value(element, value)

Returns True if value for element is within the constraints.

This method is abstract. Override in a subclass or pass a custom callable to the Constrained constructor.

adapt(value)

Given any object obj, try to coerce it into native format.

Returns:the native format or raises AdaptationError on failure.

This abstract method is called by set().

serialize(value)

Given any object obj, coerce it into a text representation.

Returns:Must return a Unicode text object, always.

No special effort is made to coerce values not of native or a compatible type.

This semi-abstract method is called by set(). The base implementation returns str(obj) (or unicode).

Enum

class Enum(value=Unspecified, **kw)

Bases: flatland.schema.scalars.Constrained

A scalar type with a limited set of allowed values.

By default values are strings, but can be of any type you like by customizing child_type.

valued(*enum_values)

Return a class with valid_values = enum_values

Parameters:*enum_values – zero or more values for valid_values. Returns:a new class

valid_values = ()

Valid element values.

Attempting to set() a value not present in valid_values will cause an adaptation failure, and value will be None.

valid_value(element, value)

True if value is within valid_values.

Compound Fields

class DateYYYYMMDD(value=Unspecified, **kw)

Bases: flatland.schema.compound.Compound, flatland.schema.scalars.Date

compose()

Return a text, native tuple built from children’s state.

Returns:a 2-tuple of text representation, native value. These correspond to the serialize_element() and adapt_element() methods of Scalar objects.

For example, a compound date field may return a ‘-‘ delimited string of year, month and day digits and a datetime.date.

explode(value)

Given a compound value, assign values to children.

Parameters:value – a value to be adapted and exploded

For example, a compound date field may read attributes from a datetime.date value and set() them on child fields.

The decision to perform type checking on value is completely up to you and you may find you want different rules for different compound types.

class JoinedString(value=Unspecified, **kw)

Bases: flatland.schema.containers.Array, flatland.schema.scalars.String

A sequence container that acts like a compounded string such as CSV.

Marshals child element values to and from a single string:

>>> from flatland import JoinedString
>>> el = JoinedString(['x', 'y', 'z'])
>>> el.value
u'x,y,z'
>>> el2 = JoinedString('foo,bar')
>>> el2[1].value
u'bar'
>>> el2.value
u'foo,bar'

Only the joined representation is considered when flattening or restoring with set_flat(). JoinedStrings run validation after their children.

separator = u','

The string used to join children’s u representations. Will also be used to split incoming strings, unless separator_regex is also defined.

separator_regex = None

Optional, a regular expression, used preferentially to split an incoming separated value into components. Used in combination with separator, a permissive parsing policy can be combined with a normalized representation, e.g.:

>>> import re
>>> schema = JoinedString.using(separator=', ',
...                             separator_regex=re.compile('\s*,\s*'))
...
>>> schema('a  ,  b,c,d').value
u'a, b, c, d'

member_schema

alias of flatland.schema.scalars.String

set(value)

Assign the native and Unicode value.

Attempts to adapt the given iterable and assigns this element’s value and u attributes in tandem. Returns True if the adaptation was successful. See Element.set().

Set must be supplied a Python sequence or iterable:

>>> from flatland import Integer, List
>>> Numbers = List.of(Integer)
>>> nums = Numbers()
>>> nums.set([1, 2, 3, 4])
True
>>> nums.value
[1, 2, 3, 4]

value

A read-only separator-joined string of child values.

u

A read-only separator-joined string of child values.

Advanced Usage

References

class Ref(value=Unspecified, **kw)

Bases: flatland.schema.scalars.Scalar

adapt(value)

Given any object obj, try to coerce it into native format.

Returns:the native format or raises AdaptationError on failure.

This abstract method is called by set().

serialize(value)

Given any object obj, coerce it into a text representation.

Returns:Must return a Unicode text object, always.

No special effort is made to coerce values not of native or a compatible type.

This semi-abstract method is called by set(). The base implementation returns str(obj) (or unicode).

u

The text representation of the reference target.

value

The native value representation of the reference target.

Validation

Basic Validation

All elements support validation. The default, built-in validation logic is simple: if the element is empty, it is invalid. Otherwise it is valid.

If that sounds too simple don’t worry- you can customize validation to suit your needs.

Validating an Element

>>> from flatland import String
>>> form = String()
>>> form.is_empty
True
>>> form.valid
Unevaluated
>>> form.validate()
False
>>> form.valid
False

Validation sets the valid attribute of each element it inspects. validate() may be invoked more than once.

>>> form.set('Squiznart')
True
>>> form.is_empty
False
>>> form.validate()
True
>>> form.valid
True

Note that default validation does not set any error messages that might be displayed to an interactive user. Messages are easily added through custom validation.

Validating Entire Forms At Once

validate() is recursive by default. Called on a parent node, it will descend through all of its children, validating each. If the parent or any one of its children are invalid, validate returns false. Note that recursion does not stop if it finds an invalid child: all children are evaluated, and each will have its valid attribute updated.

Optional Elements

If an element is marked as optional, it is exempt from validation when empty. With the default validation strategy, this effectively means that element can never be invalid. With custom validation, optional fields become more useful.

>>> from flatland import Dict, Integer
>>> schema = Dict.of(Integer.named('x'),
...                  Integer.named('y'),
...                  Integer.named('z').using(optional=True))
>>> form = schema(dict(x=1))
>>> form.validate()
False
>>> form.valid
True
>>> form['x'].valid
True
>>> form['y'].valid
False
>>> form['z'].valid
True

Validation Signals

The flatland.signals.validator_validated signal is emitted each time a validator evaluates an element. The signal’s sender is the validator (or the symbol flatland.validation.NotEmpty for the default validation strategy). The signal also sends the element, the state, and the result of the validation function.

During development, it can be convenient to connect the validator_validated signal to a logging function to aid in debugging.

from flatland.signals import validator_validated

@validator_validated.connect
def monitor_validation(sender, element, state, result):
    # print or logging.debug validations as they happen:
    print("validation: %s(%s) valid == %r" % (
      sender, element.flattened_name(), result))

>>> from flatland import String
>>> form = String(name='surname')
>>> form.validate()
validation: NotEmpty(surname) valid == False
False

Custom Validation

The default validation support is useful for some tasks, however in many cases you will want to provide your own validation rules tailored to your schema.

Flatland provides a low level interface for custom validation logic, based on a simple callable. Also provided is a higher level, class-based interface that provides conveniences for messaging, i18n and validator reuse. A library of commonly needed validators is included.

Custom Validation Basics

To use custom validation, assign a list of one or more validators to a field’s validators attribute. Each validator will be evaluated in sequence until a validator returns false or the list of validators is exhausted. If the list is exhausted and all have returned true, the element is considered valid.

A validator is a callable of the form:

validator(element, state) → bool

element is the element being validated, and state is the value passed into validate(), which defaults to None.

A typical validator will examine the value of the element:

def no_shouting(element, state):
    """Disallow ALL CAPS TEXT."""
    if element.value.isupper():
        return False
    else:
        return True

# Try out the validator
from flatland import String
form = String(validators=[no_shouting])
form.set('OH HAI')
assert not form.validate()
assert not form.valid

Validation Phases

There are two phases when validating an element or container of elements. First, each element is visited once descending down the container, breadth-first. Then each is visited again ascending back up the container.

The simple, scalar types such as String and Integer process their validators on the descent phase. The containers, such as Form and List process validators on the ascent phase.

The upshot of the phased evaluation is that container validators fire after their children, allowing container validation logic that considers the validity and status of child elements.

>>> from flatland import Dict, String
>>> def tattle(element, state):
...     print(element.name)
...     return True
...
>>> schema = (Dict.named('outer').
...                of(String.named('inner').
...                          using(validators=[tattle])).
...                using(validators=[tattle]))
>>> form = schema()
>>> form.validate()
inner
outer
True

Short-Circuiting Descent Validation

Descent validation can be aborted early by returning SkipAll or SkipAllFalse from a validator. Children will not be validated or have their valid attribute assigned. This capability comes in handy in a web environment when designing rich UIs.

Containers will run any validators in their descent_validators list during the descent phase. Descent validation is the only phase that may be short-circuited.

>>> from flatland import Dict, SkipAll, String
>>> def skip_children(element, state):
...     return SkipAll
...
>>> def always_fail(element, state):
...     return False
...
>>> schema = Dict.of(String.named('child').using(validators=[always_fail])).\
...               using(descent_validators=[skip_children])
>>> form = schema()
>>> form.validate()
True
>>> form['child'].valid
Unevaluated

Messaging

A form that fails to submit without a clear reason is frustrating. Messages may be stashed in the errors and warnings lists on elements. In your UI or template code, these can be used to flag individual form elements that failed validation and the reason(s) why.

def no_shouting(element, state):
    """Disallow ALL CAPS TEXT."""
    if element.value.isupper():
        element.errors.append("NO SHOUTING!")
        return False
    else:
        return True

See also add_error(), a wrapper around errors.append that ensures that identical messages aren’t added to an element more than once.

A powerful and i18n-capable interface to validation and messaging is available in the higher level Validation API.

Normalization

If you want to tweak the element’s value or u string representation, validators are free to assign directly to those attributes. There is no special enforcement of assignment to these attributes, however the convention is to consider them immutable outside of normalizing validators.

Validation state

validate() accepts an optional state argument. state can be anything you like, such as a dictionary, an object, or a string. Whatever you choose, it will be supplied to each and every validator that’s called.

state can be a convenient way of passing transient information to validators that require additional information to make their decision. For example, in a web environment, one may need to supply the client’s IP address or the logged-in user for some validators to function.

A dictionary is a good place to start if you’re considering passing information in state. None of the validators that ship with flatland access state, so no worries about type conflicts there.

class User(object):
    """A mock website user class."""

    def check_password(self, plaintext):
        """Mock comparing a password to one stored in a database."""
        return plaintext == 'secret'

def password_validator(element, state):
    """Check that a field matches the user's current password."""
    user = state['user']
    return user.check_password(element.value)

from flatland import String
form = String(validators=[password_validator])
form.set('WrongPassword')
state = dict(user=User())
assert not form.validate(state)

Examining Other Elements

Element provides a rich API for accessing a form’s members, an element’s parents, children, etc. Writing simple validators such as requiring two fields to match is easy, and complex validations are not much harder.

def passwords_must_match(element, state):
    """Both password fields must match for a password change to succeed."""
    if element.value == element.find('../password2', single=True).value:
        return True
    element.errors.append("Passwords must match.")
    return False

from flatland import Form, String
class ChangePassword(Form):
    password = String.using(validators=[passwords_must_match])
    password2 = String
    new_password = String

form = ChangePassword()
form.set({'password': 'foo', 'password2': 'f00', 'new_password': 'bar'})
assert not form.validate()
assert form['password'].errors

Short-Circuiting Validation

To stop validation of an element & skip any remaining members of flatland.Element.validators, return flatland.Skip from the validator:

from flatland import Skip

def succeed_early(element, state):
    return Skip

def always_fails(element, state):
    return False

from flatland import String
form = String(validators=[succeed_early, always_fails])
assert form.validate()

Above, always_fails is never invoked.

To stop validation early with a failure, simply return False.

Validator API

The Validator class implements the validator callable interface and adds conveniences for messaging, internationalization, and customization.

To use it, subclass Validator and implement validate().

from flatland.validation import Validator

class NoShouting(Validator):
    """Disallow ALL CAPS TEXT."""

    has_shouting = "NO SHOUTING in %(label)s, please."

    def validate(self, element, state):
        if element.value.isupper():
            self.note_error(element, state, 'has_shouting')
            return False
        return True

from flatland import String

schema = String.using(validators=[NoShouting()])

Above is a Validator version of the basic Customizing Validators example. In this version, the flatland.validation.Validator.note_error() method allows the messaging to be separated from the validation logic. note_error has some useful features, including templating and automatic I18N translation.

Customizing Validators

The base constructor of the Validator class has a twist that makes customizing existing Validators on the fly a breeze. The constructor can be passed keyword arguments matching any class attribute, and they will be overridden on the instance.

schema = String.using(validators=[NoShouting(has_shouting='shh.')])

Subclassing achieves the same effect.

class QuietPlease(NoShouting):
    has_shouting = 'shh.'

schema = String.using(validators=[QuietPlease()])

The validators that ship with Flatland place all of their messaging and as much configurable behavior as possible in class attributes to support easy customization.

Message Templating

Messages prepared by Validator.note_error() and Validator.note_warning() may be templated using keywords in the sprintf-style Python string format syntax.

Possible keys are taken from multiple sources. In order of priority:

• Keyword arguments sent to the note_error and note_warning methods.
• Elements of state, if state is dict-like or supports [index] access.
• Attributes of state.
• Attributes of the Validator instance.
• Attributes of the element.

Message Pluralization

Flatland supports ngettext-style message pluralization. For this style, messages are specified as a 3-tuple of (singular message, plural message, n-key). n_key is any valid templating keyword, and its value n will be looked up using the same resolution rules. If the value n equals 1, the singular form will be used. Otherwise the plural.

from flatland.validation import Validator

class MinLength(Validator):

    min_length = 2

    too_short = (
      "%(label)s must be at least one character long.",
      "%(label)s must be at least %(min_length)s characters long.",
      "min_length")

    def validate(self, element, state):
        if len(element.value) < self.min_length:
            self.note_error(element, state, "too_short")
            return False
        return True

Conditional pluralization functions with or without I18N configured.

Message Internationalization

Messages can be translated using gettext-compatible functions. Translation works in conjunction with message templating features: the message itself is translated, and strings substituted into the message are also translated individually.

Translation uses ugettext and optionally ungettext functions that you provide. You may place these functions in the state, place them on the element or its schema, or place them in Python’s builtins.

An element’s ancestry will be searched for these functions. If you like, you may assign them solely to the top-most element or its schema and they will be used to translate all of its child elements.

If you opt to supply ugettext but not ungettext, Flatland’s built-in pluralization will kick in if a pluralized message is found. Flatland will choose the correct form internally, and the result will be fed through ugettext for translation.

Dynamic Messages

Dynamic generated messages can also take advantage of the templating and internationalization features. There are two options for dynamic messages through Validator.note_error() and Validator.note_warning():

1. Supply the message directly to note_error using message="..." instead of a message key.
2. Messages looked up by key may also be callables. The callable will be invoked with element and state, and should return either a message string or a 3-tuple as described in pluralization.

The Validator Class

class Validator(**kw)

Base class for fancy validators.

Construct a validator.

Parameters:**kw – override any extant class attribute on this instance.

validate(element, state)

Validate an element returning True if valid.

Abstract.

Parameters:

• element – an Element instance.
• state – an arbitrary object. Supplied by Element.validate.

Returns:

True if valid

note_error(element, state, key=None, message=None, **info)

Record a validation error message on an element.

Parameters:

• element – An Element instance.
• state – an arbitrary object. Supplied by Element.validate.
• key – semi-optional, default None. The name of a message-holding attribute on this instance. Will be used to message = getattr(self, key).
• message – semi-optional, default None. A validation message. Use to provide a specific message rather than look one up by key.
• **info – optional. Additional data to make available to validation message string formatting.

Returns:

False

Either key or message is required. The message will have formatting expanded by expand_message() and be appended to element.errors.

Always returns False. This enables a convenient shorthand when writing validators:

from flatland.validation import Validator

class MyValidator(Validator):
    my_message = 'Oh noes!'

    def validate(self, element, state):
        if not element.value:
            return self.note_error(element, state, 'my_message')
        else:
            return True

note_warning(element, state, key=None, message=None, **info)

Record a validation warning message on an element.

Parameters:

• element – An Element instance.
• state – an arbitrary object. Supplied by Element.validate.
• key – semi-optional, default None. The name of a message-holding attribute on this instance. Will be used to message = getattr(self, key).
• message – semi-optional, default None. A validation message. Use to provide a specific message rather than look one up by key.
• **info – optional. Additional data to make available to validation message string formatting.

Returns:

False

Either key or message is required. The message will have formatting expanded by expand_message() and be appended to element.warnings.

Always returns False.

find_transformer(type, element, state, message)

Locate a message-transforming function, such as ugettext.

Returns None or a callable. The callable must return a message. The call signature of the callable is expected to match ugettext or ungettext:

• If type is ‘ugettext’, the callable should take a message as a positional argument.
• If type is ‘ungettext’, the callable should take three positional arguments: a message for the singular form, a message for the plural form, and an integer.

Subclasses may override this method to provide advanced message transformation and translation functionality, on a per-element or per-message granularity if desired.

The default implementation uses the following logic to locate a transformer:

1. If state has an attribute or item named type, return that.
2. If the element or any of its parents have an attribute named type, return that.
3. If the schema of element or the schema of any of its parents have an attribute named type, return that.
4. If type is in builtins, return that.
5. Otherwise return None.

expand_message(element, state, message, **extra_format_args)

Apply formatting to a validation message.

Parameters:

• element – an Element instance.
• state – an arbitrary object. Supplied by Element.validate.
• message –

  a string, 3-tuple or callable. If a 3-tuple, must be of the form (‘single form’, ‘plural form’, n_key).

  If callable, will be called with 2 positional arguments (element, state) and must return a string or 3-tuple.

• **extra_format_args – optional. Additional data to make available to validation message string formatting.

Returns:

the formatted string

See Message Templating, Message Pluralization and Message Internationalization for full information on how messages are expanded.

Included Validators

Scalars

class Present(**kw)

Bases: flatland.validation.base.Validator

Validates that a value is present.

Messages

missing

Emitted if the u string value of the element is empty, as in the case for an HTML form submitted with an input box left blank.

Construct a validator.

Parameters:**kw – override any extant class attribute on this instance.

validate(element, state)

Validate an element returning True if valid.

Abstract.

Parameters:

• element – an Element instance.
• state – an arbitrary object. Supplied by Element.validate.

Returns:

True if valid

class IsTrue(**kw)

Bases: flatland.validation.base.Validator

Validates that a value evaluates to true.

Messages

false

Emitted if bool(element.value) is not True.

Construct a validator.

Parameters:**kw – override any extant class attribute on this instance.

validate(element, state)

Validate an element returning True if valid.

Abstract.

Parameters:

• element – an Element instance.
• state – an arbitrary object. Supplied by Element.validate.

Returns:

True if valid

class IsFalse(**kw)

Bases: flatland.validation.base.Validator

Validates that a value evaluates to false.

Messages

true

Emitted if bool(element.value) is not False.

Construct a validator.

Parameters:**kw – override any extant class attribute on this instance.

validate(element, state)

Validate an element returning True if valid.

Abstract.

Parameters:

• element – an Element instance.
• state – an arbitrary object. Supplied by Element.validate.

Returns:

True if valid

class ValueIn(valid_options=Unspecified, **kw)

Bases: flatland.validation.base.Validator

Validates that the value is within a set of possible values.

Example:

import flatland
from flatland.validation import ValueIn

is_yesno = ValueIn(valid_options=['yes', 'no'])
schema = flatland.String('yn', validators=[is_yesno])

Attributes

valid_options

A list, set, or other container of valid element values.

Messages

fail

Emitted if the element’s value is not within the valid_options.

validate(element, state)

Validate an element returning True if valid.

Abstract.

Parameters:

• element – an Element instance.
• state – an arbitrary object. Supplied by Element.validate.

Returns:

True if valid

class Converted(**kw)

Bases: flatland.validation.base.Validator

Validates that an element was converted to a Python value.

Example:

import flatland
from flatland.validation import Converted

not_bogus = Converted(incorrect='Please enter a valid date.')
schema = flatland.DateTime('when', validators=[not_bogus])

Messages

incorrect

Emitted if the value is None.

Construct a validator.

Parameters:**kw – override any extant class attribute on this instance.

validate(element, state)

Validate an element returning True if valid.

Abstract.

Parameters:

• element – an Element instance.
• state – an arbitrary object. Supplied by Element.validate.

Returns:

True if valid

class ShorterThan(maxlength=Unspecified, **kw)

Bases: flatland.validation.base.Validator

Validates the length of an element’s string value is less than a bound.

Example:

import flatland
from flatland.validation import ShorterThan

valid_length = ShorterThan(8)
schema = flatland.String('password', validators=[valid_length])

Attributes

maxlength

A maximum character length for the u.

This attribute may be supplied as the first positional argument to the constructor.

Messages

exceeded

Emitted if the length of the element’s string value exceeds maxlength.

validate(element, state)

Validate an element returning True if valid.

Abstract.

Parameters:

• element – an Element instance.
• state – an arbitrary object. Supplied by Element.validate.

Returns:

True if valid

NoLongerThan

alias of flatland.validation.scalars.ShorterThan

class LongerThan(minlength=Unspecified, **kw)

Bases: flatland.validation.base.Validator

Validates the length of an element’s string value is more than a bound.

Example:

import flatland
from flatland.validation import LongerThan

valid_length = LongerThan(4)
schema = flatland.String('password', validators=[valid_length])

Attributes

minlength

A minimum character length for the u.

This attribute may be supplied as the first positional argument to the constructor.

Messages

short

Emitted if the length of the element’s string value falls short of minlength.

validate(element, state)

Validate an element returning True if valid.

Abstract.

Parameters:

• element – an Element instance.
• state – an arbitrary object. Supplied by Element.validate.

Returns:

True if valid

class LengthBetween(minlength=Unspecified, maxlength=Unspecified, **kw)

Bases: flatland.validation.base.Validator

Validates the length of an element’s string value is within bounds.

Example:

import flatland
from flatland.validation import LengthBetween

valid_length = LengthBetween(4, 8)
schema = flatland.String('password', validators=[valid_length])

Attributes

minlength

A minimum character length for the u.

This attribute may be supplied as the first positional argument to the constructor.

maxlength

A maximum character length for the u.

This attribute may be supplied as the second positional argument to the constructor.

Messages

breached

Emitted if the length of the element’s string value is less than minlength or greater than maxlength.

validate(element, state)

Validate an element returning True if valid.

Abstract.

Parameters:

• element – an Element instance.
• state – an arbitrary object. Supplied by Element.validate.

Returns:

True if valid

class ValueLessThan(boundary, **kw)

Bases: flatland.validation.base.Validator

A validator that ensures that the value is less than a limit.

Example:

import flatland
from flatland.validation import ValueLessThan

schema = flatland.Integer('wishes', validators=[ValueLessThan(boundary=4)])

Attributes

boundary

Any comparable object.

Messages

failure

Emitted if the value is greater than or equal to boundary.

validate(element, state)

Validate an element returning True if valid.

Abstract.

Parameters:

• element – an Element instance.
• state – an arbitrary object. Supplied by Element.validate.

Returns:

True if valid

class ValueAtMost(maximum, **kw)

Bases: flatland.validation.base.Validator

A validator that enforces a maximum value.

Example:

import flatland
from flatland.validation import ValueAtMost

schema = flatland.Integer('wishes', validators=[ValueAtMost(maximum=3)])

Attributes

maximum

Any comparable object.

Messages

failure

Emitted if the value is greater than maximum.

validate(element, state)

Validate an element returning True if valid.

Abstract.

Parameters:

• element – an Element instance.
• state – an arbitrary object. Supplied by Element.validate.

Returns:

True if valid

class ValueGreaterThan(boundary, **kw)

Bases: flatland.validation.base.Validator

A validator that ensures that a value is greater than a limit.

Example:

import flatland
from flatland.validation import ValueGreaterThan

schema = flatland.Integer('wishes', validators=[ValueGreaterThan(boundary=4)])

Attributes

boundary

Any comparable object.

Messages

failure

Emitted if the value is greater than or equal to boundary.

validate(element, state)

Validate an element returning True if valid.

Abstract.

Parameters:

• element – an Element instance.
• state – an arbitrary object. Supplied by Element.validate.

Returns:

True if valid

class ValueAtLeast(minimum, **kw)

Bases: flatland.validation.base.Validator

A validator that enforces a minimum value.

Example:

import flatland
from flatland.validation import ValueAtLeast

schema = flatland.Integer('wishes', validators=[ValueAtLeast(minimum=3)])

Attributes

minimum

Any comparable object.

Messages

failure

Emitted if the value is less than minimum.

validate(element, state)

Validate an element returning True if valid.

Abstract.

Parameters:

• element – an Element instance.
• state – an arbitrary object. Supplied by Element.validate.

Returns:

True if valid

class ValueBetween(minimum, maximum, **kw)

Bases: flatland.validation.base.Validator

A validator that enforces minimum and maximum values.

Example:

import flatland
from flatland.validation import ValueBetween

schema = flatland.Integer('wishes',
                         validators=[ValueBetween(minimum=1, maximum=3)])

Attributes

minimum

Any comparable object.

maximum

Any comparable object.

inclusive

Boolean value indicating that minimum and maximum are included in the range. Defaults to True.

Messages

failure_inclusive

Emitted when inclusive is True if the expression minimum <= value <= maximum evaluates to False.

failure_exclusive

Emitted when inclusive is False if the expression minimum < value < maximum evaluates to False.

validate(element, state)

Validate an element returning True if valid.

Abstract.

Parameters:

• element – an Element instance.
• state – an arbitrary object. Supplied by Element.validate.

Returns:

True if valid

class MapEqual(*field_paths, **kw)

Bases: flatland.validation.base.Validator

A general field equality validator.

Validates that two or more fields are equal.

Attributes

field_paths

A sequence of field names or field paths. Path names will be evaluated at validation time and relative path names are resolved relative to the element holding this validator. See ValuesEqual for an example.

transform

A 1-arg callable, passed a Element, returning a value for equality testing.

Messages

unequal

Emitted if the transform(element) of all elements are not equal. labels will substitute to a comma-separated list of the label of all but the last element; last_label is the label of the last.

Construct a MapEqual.

Parameters:

• *field_paths – a sequence of 2 or more elements names or paths.
• **kw – passed to Validator.__init__().

validate(element, state)

Validate an element returning True if valid.

Abstract.

Parameters:

• element – an Element instance.
• state – an arbitrary object. Supplied by Element.validate.

Returns:

True if valid

class ValuesEqual(*field_paths, **kw)

Bases: flatland.validation.scalars.MapEqual

Validates that the values of multiple elements are equal.

A MapEqual that compares the value of each element.

Example:

from flatland import Schema, String
from flatland.validation import ValuesEqual

class MyForm(Schema):
    password = String
    password_again = String
    validators = [ValuesEqual('password', 'password_again')]

transform

attrgetter(‘value’)

Construct a MapEqual.

Parameters:

• *field_paths – a sequence of 2 or more elements names or paths.
• **kw – passed to Validator.__init__().

class UnisEqual(*field_paths, **kw)

Bases: flatland.validation.scalars.MapEqual

Validates that the Unicode values of multiple elements are equal.

A MapEqual that compares the u of each element.

transform

attrgetter(‘u’)

Construct a MapEqual.

Parameters:

• *field_paths – a sequence of 2 or more elements names or paths.
• **kw – passed to Validator.__init__().

Containers

class NotDuplicated(**kw)

Bases: flatland.validation.base.Validator

A sequence member validator that ensures all sibling values are unique.

Marks the second and any subsequent occurrences of a value as invalid. Only useful on immediate children of sequence fields such as flatland.List.

Example:

import flatland
from flatland.schema.containers import List
from flatland.validation import NotDuplicated

validator = NotDuplicated(failure="Please enter each color only once.")
schema = List.of(String.named('favorite_color')).\
              using(validators=[validator])

Attributes

comparator

A callable boolean predicate, by default operator.eq. Called positionally with two arguments, element and sibling.

Can be used as a filter, for example ignoring any siblings that have been marked as “deleted” by a checkbox in a web form:

from flatland import Schema, List, String, Integer, Boolean
from flatland.validation import NotDuplicated

def live_addrs(element, sibling):
    thisval, thatval = element.value, sibling.value
    # data marked as deleted is never considered a dupe
    if thisval['deleted'] or thatval['deleted']:
        return False
    # compare elements on 'street' & 'city', ignoring 'id'
    return (thisval['street'] == thatval['street'] and
            thisval['city'] == thatval['city'])

class Address(Schema):
    validators = [NotDuplicated(comparator=live_addrs)]

    id = Integer.using(optional=True)
    deleted = Boolean
    street = String
    city = String

schema = List.of(Address)

Messages

failure

Emitted on an element that has already appeared in a parent sequence. container_label will substitute the label of the container. position is the position of the element in the parent sequence, counting up from 1.

Construct a validator.

Parameters:**kw – override any extant class attribute on this instance.

comparator()

eq(a, b) – Same as a==b.

validate(element, state)

Validate an element returning True if valid.

Abstract.

Parameters:

• element – an Element instance.
• state – an arbitrary object. Supplied by Element.validate.

Returns:

True if valid

class HasAtLeast(**kw)

Bases: flatland.validation.base.Validator

A sequence validator that ensures a minimum number of members.

May be applied to a sequence type such as a List.

Example:

from flatland import List, String
from flatland.validation import HasAtLeast

schema = List.of(String.named('wish')).\
              using(validators=[HasAtLeast(minimum=3)])

Attributes

minimum

Any positive integer.

Messages

failure

Emitted if the sequence contains less than minimum members. child_label will substitute the label of the child schema.

Construct a validator.

Parameters:**kw – override any extant class attribute on this instance.

validate(element, state)

Validate an element returning True if valid.

Abstract.

Parameters:

• element – an Element instance.
• state – an arbitrary object. Supplied by Element.validate.

Returns:

True if valid

class HasAtMost(**kw)

Bases: flatland.validation.base.Validator

A sequence validator that ensures a maximum number of members.

May be applied to a sequence type such as a List.

Example:

from flatland import List, String
from flatland.validation import HasAtMost

schema = List.of(String.named('wish')).\
              using(validators=[HasAtMost(maximum=3)])

Attributes

maximum

Any positive integer.

Messages

failure

Emitted if the sequence contains more than maximum members. child_label will substitute the label of the child schema.

Construct a validator.

Parameters:**kw – override any extant class attribute on this instance.

validate(element, state)

Validate an element returning True if valid.

Abstract.

Parameters:

• element – an Element instance.
• state – an arbitrary object. Supplied by Element.validate.

Returns:

True if valid

class HasBetween(**kw)

Bases: flatland.validation.base.Validator

Validates that the number of members of a sequence lies within a range.

May be applied to a sequence type such as a List.

Example:

from flatland import List, String
from flatland.validation import HasBetween

schema = List.of(String.named('wish')).\
              using(validators=[HasBetween(minimum=1, maximum=3)])

Attributes

minimum

Any positive integer.

maximum

Any positive integer.

Messages

range

Emitted if the sequence contains fewer than minimum members or more than maximum members. child_label will substitute the label of the child schema.

exact

Like range, however this message is emitted if minimum and maximum are the same.

schema = List.of(String.named('wish')).\
              using(validators=[HasBetween(minimum=3, maximum=3)])

validate(element, state)

Validate an element returning True if valid.

Abstract.

Parameters:

• element – an Element instance.
• state – an arbitrary object. Supplied by Element.validate.

Returns:

True if valid

class SetWithKnownFields(**kw)

Bases: flatland.validation.base.Validator

A mapping validator that ensures no unexpected fields were set().

May be applied to a mapping type such as a Dict.

Example:

from flatland import Dict, Integer
from flatland.validation import SetWithKnownFields

schema = Dict.of(Integer.named('x'), Integer.named('y')).\
              validated_by(SetWithKnownFields())
schema.policy = None
element = schema()

element.set({'x': 123, 'y': 456})
assert element.validate()

element.set({'x': 123, 'y': 456, 'z': 789})
assert not element.validate()

#from flatland import Dict, Integer
#from flatland.validation import SetWithKnownFields
#
#schema = Dict.of(Integer.named('x'), Integer.named('y')).\
#              validated_by(SetWithKnownFields())
#schema.policy = None
#element = schema()
#
#element.set({'x': 123})
#assert element.validate()  # assertion error, issue #25, FIXME!
#
#element.set({'x': 123, 'z': 789})
#assert not element.validate()  # no assertion error, but maybe due to #25 also.

This validator collects the keys from raw and compares them to the allowed keys for the element. Only elements in which raw is available and iterable will be considered for validation; all others are deemed valid.

Warning

This validator will not enforce policy on mappings initialized with set_flat() because raw is unset.

Note

This validator obsoletes and deprecates the Dict.policy = 'subset' feature. During the deprecation period, policy is still enforced by set() by default. To allow this validator to run, disable the default by setting policy = None on the element or its schema.

Messages

unexpected

Emitted if the initializing value contains unexpected keys. unexpected will substitute a comma-separated list of unexpected keys, and n_unexpected a count of those keys.

Construct a validator.

Parameters:**kw – override any extant class attribute on this instance.

validate(element, state)

Validate an element returning True if valid.

Abstract.

Parameters:

• element – an Element instance.
• state – an arbitrary object. Supplied by Element.validate.

Returns:

True if valid

class SetWithAllFields(**kw)

Bases: flatland.validation.base.Validator

A mapping validator that ensures all fields were set().

May be applied to a mapping type such as a Dict.

Example:

from flatland import Dict, Integer
from flatland.validation import SetWithAllFields

schema = Dict.of(Integer.named('x'), Integer.named('y')).\
              validated_by(SetWithAllFields())
schema.policy = None
element = schema()

element.set({'x': 123, 'y': 456})
assert element.validate()

element.set({'x': 123})
assert not element.validate()

element.set({'x': 123, 'y': 456, 'z': 789})
assert not element.validate()

This validator collects the keys from raw and compares them to the allowed keys for the element. Only elements in which raw is available and iterable will be considered for validation; all others are deemed valid.

Warning

This validator will not enforce policy on mappings initialized with set_flat() because raw is unset.

Note

This validator obsoletes and deprecates the Dict.policy = 'strict' feature. During the deprecation period, policy is still enforced by set() by default. To allow this validator to run, disable the default by setting policy = None on the element or its schema.

Messages

unexpected

Emitted if the initializing value contains unexpected keys. unexpected will substitute a comma-separated list of unexpected keys, and n_unexpected a count of those keys.

missing

Emitted if the initializing value did not contain all expected keys. missing will substitute a comma-separated list of missing keys, and n_missing a count of those keys.

both

Emitted if both of the previous conditions hold, and both sets of substitution keys are available.

Construct a validator.

Parameters:**kw – override any extant class attribute on this instance.

validate(element, state)

Validate an element returning True if valid.

Abstract.

Parameters:

• element – an Element instance.
• state – an arbitrary object. Supplied by Element.validate.

Returns:

True if valid

Numbers

class Luhn10(**kw)

Bases: flatland.validation.base.Validator

True if a numeric value passes luhn10 checksum validation.

Construct a validator.

Parameters:**kw – override any extant class attribute on this instance.

validate(element, state)

Validate an element returning True if valid.

Abstract.

Parameters:

• element – an Element instance.
• state – an arbitrary object. Supplied by Element.validate.

Returns:

True if valid

luhn10_check(number)

Return True if the number passes the Luhn checksum algorithm.

Email Addresses

class IsEmail(**kw)

Bases: flatland.validation.base.Validator

Validates email addresses.

The default behavior takes a very permissive stance on allowed characters in the local-part and a relatively strict stance on the domain. Given local-part@domain:

• local-part must be present and contain at least one non-whitespace character. Any character is permitted, including international characters.
• domain must be preset, less than 253 characters and each dot-separated component must be 63 characters or less. domain may contain non-ASCII international characters, and will be converted to IDN representation before length assertions are applied. No top level domain validations are applied.

Attributes

non_local

Default True. When true, require at minimum two domain name components and reject local email addresses such as postmaster@localhost or user@workstation.

local_part_pattern

No default. If present, a compiled regular expression that will be matched to the local-part. Override this to implement more stringent checking such as RFC-compliant addresses.

domain_pattern

Defaults to a basic domain-validating regular expression with no notion of valid top level domains. Override this to require certain TLDs (or alternately and more simply, add another validator to your chain that checks the endings of the string against your list of TLDs.)

The default pattern rejects the valid but obscure quoted IP-address form ([1.2.3.4]).

Messages

invalid

Emitted if the email address is not valid.

Construct a validator.

Parameters:**kw – override any extant class attribute on this instance.

URLs

class URLValidator(**kw)

Bases: flatland.validation.base.Validator

A general URL validator.

Validates that a URL is well-formed and may optionally restrict the set of valid schemes and other URL components.

Attributes

allowed_schemes

Restrict URLs to just this sequence of named schemes, or allow all schemes with (‘*’,). Defaults to all schemes. Example:

allowed_schemes = ('http', 'https', 'ssh')

allowed_parts

A sequence of 0 or more part names in urlparse’s vocabulary:

'scheme', 'netloc', 'path', 'params', 'query', 'fragment'

Defaults to all parts allowed.

urlparse

By default the urlparse module, but may be replaced by any object that implements urlparse.urlparse() and urlparse.urlunparse().

Messages

bad_format

Emitted for an unparseable URL.

blocked_scheme

Emitted if the URL scheme: is not present in allowed_schemes.

blocked_part

Emitted if the URL has a component not present in allowed_parts.

Construct a validator.

Parameters:**kw – override any extant class attribute on this instance.

class HTTPURLValidator(**kw)

Bases: flatland.validation.base.Validator

Validates http and https URLs.

Validates that an http-like URL is well-formed and may optionally require and restrict the permissible values of its components.

Attributes

all_parts

A sequence of known URL parts. Defaults to the full 10-tuple of names in urlparse’s vocabulary for HTTP-like URLs.

required_parts

A mapping of part names. If value is True, the part is required. The value may also be a sequence of strings; the value of the part must be present in this collection to validate.

The default requires a scheme of 'http' or 'https'.

forbidden_parts

A mapping of part names. If value is True, the part is forbidden and validation fails. The value may also be a sequence of strings; the value of the part must not be present in this collection to validate.

The default forbids username and password parts.

urlparse

By default the urlparse module, but may be replaced by any object that implements urlparse.urlparse() and urlparse.urlunparse().

Messages

bad_format

Emitted for an unparseable URL.

required_part

Emitted if URL is missing a part present in required_parts.

forbidden_part

Emitted if URL contains a part present in forbidden_parts.

Construct a validator.

Parameters:**kw – override any extant class attribute on this instance.

class URLCanonicalizer(**kw)

Bases: flatland.validation.base.Validator

A URL canonicalizing validator.

Given a valid URL, re-writes it with unwanted parts removed. The default implementation drops the #fragment from the URL, if present.

Attributes

discard_parts

A sequence of 0 or more part names in urlparse’s vocabulary:

'scheme', 'netloc', 'path', 'params', 'query', 'fragment'

urlparse

By default the urlparse module, but may be replaced by any object that implements urlparse.urlparse() and urlparse.urlunparse().

Messages

bad_format

Emitted for an unparseable URL. This is impossible to hit with the Python’s standard library implementation of urlparse.

Construct a validator.

Parameters:**kw – override any extant class attribute on this instance.

HTML Forms and Markup

Flatland is not explicitly a form library, although it handles that task handily with powerful type conversion and validation error reporting. Dedicated form libraries often provide sophisticated “widget” or “control” features to render data fields as complex HTML markup with CSS and JavaScript support. The full expression of these features is outside Flatland’s scope.

However! Properly generating HTML form tags and filling them with processed data is tedious and a common need, so Flatland ships with a minimalistic yet powerful toolset for tag generation. These tools are both highly usable as-is and also a solid base for constructing higher-level widgeting systems.

Markup Generation

The generation formula is simple: a desired tag (such as input) plus a flatland Element equals a complete HTML tag with attributes like name and value filled in using the element’s state.

Operating on Element rather than the raw HTTP input or the polished final value provides a huge amount of expressive power. For example,

• Elements carry their validation errors- place these directly next to the form fields, or roll them up- your choice. Highlight failing fields with a class="error" CSS attribute right on the input element.
• (Re)populate form fields with exactly what the user typed, or the normalized version.
• Leverage the structure of the schema in template markup- if a form contains a list of 1 or more email addresses, loop over that list using your template language and render fields.
• Directly access Element properties and metadata, translation functions, and cross-element relations to implement complex view problems simply.

Flatland ships with two generator front-ends, both supporting the same features via a shared backend. The first, Generator, is for use in straight Python code, Jinja2, Mako, Genshi, or any other templating system. The second is a plugin for the Genshi templating library that integrates Flatland element binding directly and naturally into your existing <input/> tags.

Basic DWIM Binding

>>> from flatland.out.markup import Generator
>>> from flatland import Form, String
>>> html = Generator()
>>> class Login(Form):
...     username = String
...     password = String
...
>>> form = Login({'username': 'jek'})

Basic “Do What I Mean” form binding:

>>> print(html.input(form['username']))
<input name="username" value="jek" />

Likewise with Genshi.

<input form:bind="form.username"/>

and Genshi generates:

<input name="username" value="jek"/>

Attributes Too

Any HTML attribute can be included. Generated attributes can be overridden, too.

This time, the Generator is used in a Jinja2 template.

>>> from jinja2 import Template
>>> template = Template("""\
... {{ html.input(form.username, name="other", class_="custom") }}
... """)
>>> print(template.render(html=html, form=form))
<input name="other" value="jek" class="custom" />

These features are very similar in Genshi, too.

<input form:bind="form.username" name="other" class="custom"/>

Which generates the same output:

<input name="other" value="jek" class="custom"/>

Many Python templating systems allow you to replace the indexing operator (form['username']) with the attribute operator (form.username) to improve readability in templates. As shown above, this kind of rewriting trickery is generally not a problem for Flatland. Just keep name collisions in mind- if your form has a String field called name, is form.name the value of your form’s name attribute or is it the String field? When writing macros or reusable functions, using the explicit form[...] index syntax is a good choice to protect against unexpected mangling by the template system no matter what the fields are named.

And More

The tag and attribute generation behavior can be configured and even post-processed just as you like it, affecting all of your tags, just one template, a block, or even individual tags.

Controlling Attribute Transformations

Out of the box, generation will do everything required for form element rendering and repopulation: filling <textarea>s, checking checkboxes, etc. Flatland can also generate some useful optional attributes, such as id= and for= linking for <label>s. Generation of attributes is controlled with markup options at several levels:

Global:

Everything generated with a Generator instance or within a Genshi rendering operation.

Block:

Options can be overridden within the scope of a block, reverting to their previous value at the end of the block.

Tag:

Options can overridden on a per-tag basis.

Default:

Finally, each tag has a set of sane default behaviors.

Boolean options may be True, or False, “on” or “off”, or set to “auto” to revert to the transformation’s built-in default setting.

Transformations

Most transforms require a Flatland element for context, such as setting an input tag’s value= to the element’s Unicode value. These tags can be said to be “bound” to the element.

Tags need not be bound, however. Here an unbound textarea can still participate in tabindex= generation.

>>> html = Generator(tabindex=100)
>>> print(html.textarea())
<textarea></textarea>
>>> print(html.textarea(auto_tabindex=True))
<textarea tabindex="100"></textarea>
>>> html.set(auto_tabindex=True)
u''
>>> print(html.textarea())
<textarea tabindex="101"></textarea>

Setting a boolean option to “on” or True on the tag itself will always attempt to apply the transform, allowing the transform to be applied to arbitrary tags that normally would not be transformed.

>>> print(html.tag('squiznart', auto_tabindex=True))
<squiznart tabindex="102" />

The Python APIs and the Generator tags use “_”-separated transform names (valid Python identifiers) as shown below, however please note that Genshi uses XML-friendly “-“-separated attribute names in markup.

auto-name

Default:on Tags:button, form, input, select, textarea

Sets the tag name= to the bound element’s .name. Takes no action if the tag already contains a name= attribute, unless forced.

Receives a name= attribute:

>>> print(html.input(form['username'], type="text"))
<input type="text" name="username" value="jek" />

Uses the explicitly provided name="foo":

>>> print(html.input(form['username'], type="text", name='foo'))
<input type="text" name="foo" value="jek" />

Replaces name="foo" with the element’s name:

>>> print(html.input(form['username'], type="text", name='foo', auto_name=True))
<input type="text" name="username" value="jek" />

auto-value

Default:on Tags:button, input, select, textarea

Uses the bound element’s .u Unicode value for the tag’s value. The semantics of “value” vary by tag.

<input> types text, hidden, button, submit and reset:

Sets the value="" attribute of the tag, or omits the attribute if .u is the empty string.

Receives a value= attribute:

>>> print(html.input(form['username'], type="text"))
<input type="text" name="username" value="jek" />

Uses the explicitly provided value="quux":

>>> print(html.input(form['username'], type="text", value='quux'))
<input type="text" name="username" value="quux" />

<input> types password, image and file:

No value is added unless forced by setting auto_value on the tag.

>>> print(html.input(form['password'], type="password"))
<input type="password" name="password" />

But this behavior can be forced:

>>> print(html.input(form['password'], type="password", auto_value=True))
<input type="password" name="password" value="secret" />

<input> type radio:

Radio buttons will add a checked="checked" attribute if the literal value= matches the element’s value. Or, if the bind is a Container, value= will be compared against the .u of each of the container’s children until a match is found.

If the tag lacks a value= attribute, no action is taken.

>>> print(form['username'].u)
jek
>>> print(html.input(form['username'], type="radio", value="quux"))
<input type="radio" name="username" value="quux" />
>>> print(html.input(form['username'], type="radio", value="jek"))
<input type="radio" name="username" value="jek" checked="checked" />

<input> type checkbox:

Check boxes will add a checked="checked" attribute if the literal value= matches the element’s value.

>>> print(form['username'].u)
jek
>>> print(html.input(form['username'], type="checkbox", value="quux"))
<input type="checkbox" name="username" value="quux" />
>>> print(html.input(form['username'], type="checkbox", value="jek"))
<input type="checkbox" name="username" value="jek" checked="checked" />

Or, if the bind is a Container, value= will be compared against the .u of each of the container’s children until a match is found.

>>> from flatland import Array
>>> Bag = Array.named('bag').of(String)
>>> bag = Bag(['a', 'c'])
>>> for value in 'a', 'b', 'c':
...     print(html.input(bag, type="checkbox", value=value))
...
<input type="checkbox" name="bag" value="a" checked="checked" />
<input type="checkbox" name="bag" value="b" />
<input type="checkbox" name="bag" value="c" checked="checked" />

If the tag lacks a value= attribute, no action is taken, unless the bind is a Boolean. The missing value= will be added using the schema’s Boolean.true value.

>>> print(html.input(form['username'], type="checkbox"))
<input type="checkbox" name="username" />
>>> from flatland import Boolean
>>> toggle = Boolean.named('toggle')()
>>> print(html.input(toggle, type="checkbox"))
<input type="checkbox" name="toggle" value="1" />
>>> toggle.set(True)
True
>>> print(html.input(toggle, type="checkbox"))
<input type="checkbox" name="toggle" value="1" checked="checked" />
>>> toggle.true = "yes"

<input> types unknown:

For types unknown to flatland, no value is set unless forced by setting form:auto-value="on" on the tag.

<textarea>:

Textareas will insert the Element.u inside the tag pair. Content supplied with contents= for Generators or between Genshi tags will be preferred unless forced.

>>> print(html.textarea(form['username']))
<textarea name="username">jek</textarea>
>>> print(html.textarea(form['username'], contents="quux"))
<textarea name="username">quux</textarea>

Note that in Genshi, these two forms are equivalent.

<!-- these: -->
<textarea form:bind="form.username"/>
<textarea form:bind="form.username"></textarea>

<!-- will both render as -->
<textarea name="username">jek</textarea>

<select>:

Select tags apply a selected="selected" attribute to their <option> tags that match the Element.u or, if the bind is a Container, the .u of one of its children.

For this matching to work, the <option> tags must have a literal value set in the markup. The value may an explicit value= attribute, or it may be the text of the tag. Leading and trailing whitespace will be stripped when considering the text of the tag as the value.

The below will emit selected="selected" if form.field is equal to any of “a”, “b”, “c”, and “d”.

<select form:bind="form.field">
   <option>a</option>
   <option value="b"/>
   <option value="c">label</option>
   <option>
     d
   </option>
</select>

<button/> and <button value=""/>:

Regular <button/> tags will insert the Element.u inside the <button></button> tag pair. The output will not be XML-escaped, allowing any markup in the .u to render properly.

If the tag contains a literal value= attribute and a value override is forced by setting form:auto-value="on", the .u will be placed in the value= attribute, replacing the existing content. The value is escaped in this case.

<!-- set or replace the inner *markup* -->
<button form:bind="form.field"/>
<button form:bind="form.field" form:auto-value="on">xyz</button>

<!-- set the value, retaining the value= style used in the original -->
<button form:bind="form.field" value="xyz" form:auto-value="on"/>

auto-domid

Default:off Tags:button, input, select, textarea

Sets the id= attribute of the tag. Takes no action if the markup already contains a id= unless forced by setting form:auto-domid="on".

The id is generated by combining the bound element’s flattened_name with the domid-format in the current scope. The default format is f_%s.

auto-for

Default:on Tags:label

Sets the for= attribute of the tag to the id of the bound element. The id is generated using the same process as auto-domid. No consistency checks are performed on the generated id value.

Defaults to “on”, and will only apply if auto-domid is also “on”. Takes no action if the markup already contains a id= unless forced by setting form:auto-for="on".

<form:with auto-domid="on">
  <fieldset py:with="field=form.field">
    <label form:bind="field">${field.label.x}</label>
    <input type="text" form:bind="field"/>
  </fieldset>
</form:with>

auto-tabindex

Default:off Tags:button, input, select, textarea

Sets the tabindex attribute of tags with an incrementing integer.

Numbering starts at the scope’s tabindex, which has no default. Assigning a value for tabindex will set the value for the next tabindex assignment, and subsequent assignments will increment by one.

A tabindex value of 0 will block the assignment of a tabindex and will not be incremented.

Takes no action if the markup already contains a tabindex= unless forced by setting form:auto-tabindex="on".

<form:with auto-tabindex="on" tabindex="1">
  <!-- assigns tabindex="1" -->
  <input type="text" form:bind="form.field"/>

  <!-- leaves existing tabindex in place -->
  <input type="text" tabindex="-1" form:bind="form.field"/>

  <!-- assigns tabindex="2" -->
  <a href="#" form:auto-tabindex="on"/>
</form:with>

Generator

class Generator(markup=u'xhtml', **settings)

General XML/HTML tag generator

Create a generator.

Accepts any Transformations, as well as the following:

Parameters:

• markup – tag output style: 'xml', 'xhtml' or 'html'
• ordered_attributes – if True (default), output markup attributes in a predictable order. Useful for tests and generally a little more pleasant to read.

begin(**settings)

Begin a new Transformations context.

Puts **settings into effect until a matching end() is called. Each setting specified will mask the current value, reverting when end() is called.

end()

End a Transformations context.

Restores the settings that were in effect before begin().

set(**settings)

Change the Transformations in effect.

Change the **settings in the current scope. Changes remain in effect until another set() or a end() ends the current scope.

form

Generate a <form/> tag.

Parameters:

• bind – optional, a flatland element.
• **attributes – any desired XML/HTML attributes.

Returns:

a printable Tag

If provided with a bind, form tags can generate the name attribute.

input

Generate an <input/> tag.

Parameters:

• bind – optional, a flatland element.
• **attributes – any desired XML/HTML attributes.

Returns:

a printable Tag

If provided with a bind, input tags can generate the name, value and id attributes. Input tags support tabindex attributes.

textarea

Generate a <textarea/> tag.

Parameters:

• bind – optional, a flatland element.
• **attributes – any desired XML/HTML attributes.

Returns:

a printable Tag

If provided with a bind, textarea tags can generate the name and id attributes. If the bind has a value, it will be used as the tag body. Textarea tags support tabindex attributes. To provide an alternate tag body, either supply contents or use the open() and close() method of the returned tag.

button

Generate a <button/> tag.

Parameters:

• bind – optional, a flatland element.
• **attributes – any desired XML/HTML attributes.

Returns:

a printable Tag

If provided with a bind, button tags can generate the name, value, and id attributes. Button tags support tabindex attributes.

select

Generate a <select/> tag.

Parameters:

• bind – optional, a flatland element.
• **attributes – any desired XML/HTML attributes.

Returns:

a printable Tag

If provided with a bind, select tags can generate the name and id attributes. Select tags support tabindex attributes.

option

Generate an <option/> tag.

Parameters:

• bind – optional, a flatland element.
• **attributes – any desired XML/HTML attributes.

Returns:

a printable Tag

If provided with a bind, option tags can generate the value attribute. To provide tag body, either supply contents or use the open() and close() method of the returned tag:

print(generator.option.open(style='bold'))
print('<strong>contents</strong>')
print(generator.option.close())

label

Generate a <label/> tag.

Parameters:

• bind – optional, a flatland element.
• **attributes – any desired XML/HTML attributes.

Returns:

a printable Tag

If provided with a bind, label tags can generate the for attribute and fill in the tag body with the element’s label, if present.

tag(tagname, bind=None, **attributes)

Generate any tag.

Parameters:

• tagname – the name of the tag.
• bind – optional, a flatland element.
• **attributes – any desired XML/HTML attributes.

Returns:

a printable Tag

The attribute rules appropriate for tagname will be applied. For example, tag('input') is equivalent to input().

class Tag(tagname, context, dangle, paired)

A printable markup tag.

Tags are generated by Generator and are usually called immediately, returning a fully formed markup string:

print(generator.textarea(contents="hello!"))

For more fine-tuned control over your markup, you may instead choose to use the open() and close() methods of the tag:

print(generator.textarea.open())
print("hello!")
print(generator.textarea.close())

open(bind=None, **attributes)

Return the opening half of the tag, e.g. <p>.

Parameters:

• bind – optional, a flatland element.
• **attributes – any desired tag attributes.

close()

Return the closing half of the tag, e.g. </p>.

Genshi Directives

http://ns.discorporate.us/flatland/genshi

Signals

Flatland can notify your code when events of interest occur during flatland processing using Blinker signals. These signals can be used for advanced customization in your application or simply as a means for tracing and logging flatland activity during development.

element_set = <blinker.base.NamedSignal object at 0x7ff9b46e4e50; 'element_set'>

Emitted after set() has been called on an element.

Parameters:

• sender – the element
• adapted – boolean, True if the set() adapted successfully.

validator_validated = <blinker.base.NamedSignal object at 0x7ff9b46e4e90; 'validator_validated'>

Emitted after a validator has processed an element.

Parameters:

• sender – the validator callable doing validation
• element – the element being validated
• state – the state passed to validate()
• result – the result of validator execution

Patterns

Widgets using Templates and Schema Properties

Unlike utilities more directly focused on processing Web forms, Flatland does not include any concept of “widgets” that render a field. It is however easy enough to employ Flatland’s “properties” and markup generation support to build our own widget system. This also gives us complete control over the rendering.

from flatland import Form, String

Input = String.with_properties(widget='input', type='text')
Password = Input.with_properties(type='password')

class SignInForm(Form):
    username = Input.using(label='Username')
    password = Password.using(label='Password')

Rendering Widgets with Genshi

Macros via Genshi’s py:def directive would be a good way to implement the actual widgets. For example:

<html
    xmlns:form="http://ns.discorporate.us/flatland/genshi"
    xmlns:py="http://genshi.edgewall.org/"
    py:strip=""
  >

  <py:def
      function="widget(field)"
      py:with="macro = value_of(field.properties.widget + '_widget')"
      py:replace="macro(field)"
    />

  <fieldset py:def="input_widget(field)">
    <form:with
        auto-domid="on"
        auto-for="on"
      >

      <label
          form:bind="field"
          py:content="field.label"
        />

      <input
          form:bind="field"
          type="${field.properties.type}"
        />

    </form:with>
  </fieldset>
</html>

Typically we would call the widget macro manually for each field we want rendered, and in the desired order, but for demonstrative purposes we stub out widgets for each field in arbitrary order:

<html
    xmlns:py="http://genshi.edgewall.org/"
    xmlns:xi="http://www.w3.org/2001/XInclude"
  >
  <xi:include href="widgets.html"/>
  <body>
    <form>
      ${widget(form['username'])}
      ${widget(form['password'])}
    </form>
  </body>
</html>

Rendering with Jinja

If you’re not using Genshi you can still benefit from Flatland’s schema-aware markup generating support. With Jinja we might implement the macros as something resembling this:

{% set html = form_generator %}

{% macro widget(field) %}
  {%- set macro = {'input': input}[field.properties.widget] -%}
  {{- macro(field) -}}
{% endmacro %}

{% macro input(field) %}
  {%- do html.begin(auto_domid=true, auto_for=true) %}
<fieldset>
  {{ html.label(field, contents=field.label) }}
  {{ html.input(field, type=field.properties.type) }}
</fieldset>
  {%- do html.end() %}
{% endmacro %}

Then we can simply import the widget macro to form templates:

{% from 'widgets.html' import widget -%}
<html>
  <body>
    <form>
      {{- widget(form['username']) }}
      {{- widget(form['password']) }}
    </form>
  </body>
</html>

Make sure to add a markup generator to the globals of your Jinja environment:

from flatland.out.markup import Generator
jinja_env.globals['form_generator'] = Generator('html')

API

class Scalar(value=Unspecified, **kw)

Bases: flatland.schema.base.Element

The base implementation of simple values such as a string or number.

Scalar subclasses are responsible for translating the most common data types in and out of Python-native form: strings, numbers, dates, times, Boolean values, etc. Any data which can be represented by a single (name, value) pair is a likely Scalar.

Scalar subclasses have two responsibilities: provide a method to adapt a value to native Python form, and provide a method to serialize the native form to a string.

This class is abstract.

set(obj)

Process obj and assign the native and text values.

Returns:True if adaptation of obj was successful.

Attempts to adapt the given object and assigns this element’s value and u attributes in tandem.

If adaptation succeeds, .value will contain the adapted native Python value and .u will contain a text serialized version of it. A native value of None will be represented as u'' in .u.

If adaptation fails, .value will be None and .u will contain str(obj) (or unicode), or u'' for none.

adapt(obj)

Given any object obj, try to coerce it into native format.

Returns:the native format or raises AdaptationError on failure.

This abstract method is called by set().

serialize(obj)

Given any object obj, coerce it into a text representation.

Returns:Must return a Unicode text object, always.

No special effort is made to coerce values not of native or a compatible type.

This semi-abstract method is called by set(). The base implementation returns str(obj) (or unicode).

set_default()

set() the element to the schema default.

class Number(value=Unspecified, **kw)

Bases: flatland.schema.scalars.Scalar

Base for numeric fields.

Subclasses provide type_ and format attributes for adapt() and serialize().

type_ = None

The Python type for values, such as int or float.

signed = True

If true, allow negative numbers. Default True.

format = u'%s'

The text serialization format.

adapt(value)

Generic numeric coercion.

Returns:an instance of type_ or None

Attempt to convert value using the class’s type_ callable.

serialize(value)

Generic numeric serialization.

Returns:Unicode text formatted with format or the str() (or unicode) of value if value is not of type_

Converts value to a string using Python’s string formatting function and the format as the template. The value is provided to the format as a single, positional format argument.

class Temporal(value=Unspecified, **kw)

Bases: flatland.schema.scalars.Scalar

Base for datetime-based date and time fields.

type_

Abstract. The native type for element values, will be called with positional arguments per used below.

regex

Abstract. A regular expression to parse datetime values from a string. Must supply named groupings.

used

Abstract. A sequence of regex match group names. These matches will be converted to ints and supplied to the type_ constructor in the order specified.

format

Abstract. A Python string format for serializing the native value. The format will be supplied a dict containing all attributes of the native type.

adapt(value)

Coerces value to a native type.

If value is an instance of type_, returns it unchanged. If a string, attempts to parse it and construct a type as described in the attribute documentation.

serialize(value)

Serializes value to string.

If value is an instance of type, formats it as described in the attribute documentation. Otherwise returns str(value) (or unicode).

class Container(value=Unspecified, **kw)

Bases: flatland.schema.base.Element

Holds other schema items.

Base class for elements that can contain other elements, such as List and Dict.

Parameters:

• descent_validators – optional, a sequence of validators that will be run before contained elements are validated.
• validators – optional, a sequence of validators that will be run after contained elements are validated.
• **kw – other arguments common to Element.

descent_validators = ()

Todo

doc descent_validators

descent_validated_by(*validators)

Return a class with descent validators set to *validators.

Parameters:*validators – one or more validator functions, replacing any descent validators present on the class. Returns:a new class

including_descent_validators(*validators, **kw)

Return a class with additional descent *validators.

Parameters:

• *validators – one or more validator functions
• position – defaults to -1. By default, additional validators are placed after existing descent validators. Use 0 for before, or any other list index to splice in validators at that point.

Returns:

a new class

class Sequence(value=Unspecified, **kw)

Bases: flatland.schema.containers.Container, list

Abstract base of sequence-like Containers.

Instances of Sequence hold other elements and operate like Python lists. Each sequence member will be an instance of member_schema.

Python list methods and operators may be passed instances of member_schema or plain Python values. Using plain values is a shorthand for creating an member_schema instance and set()ting it with the value:

>>> from flatland import Array, Integer
>>> Numbers = Array.of(Integer)
>>> ones = Numbers()
>>> ones.append(1)
>>> ones
[<Integer None; value=1>]
>>> another_one = Integer()
>>> another_one.set(1)
True
>>> ones.append(another_one)
>>> ones
[<Integer None; value=1>, <Integer None; value=1>]

member_schema = None

An Element class for sequence members.

prune_empty = True

If true, skip missing index numbers in set_flat(). Default True.

See `Sequences`_ for more information.

of(*schema)

Declare the class to hold a sequence of *schema.

Params *schema:one or more Element classes Returns:cls

Configures the member_schema of cls to hold instances of *schema.

>>> from flatland import Array, String
>>> Names = Array.of(String.named('name'))
>>> Names.member_schema
<class 'flatland.schema.scalars.String'>
>>> el = Names(['Bob', 'Biff'])
>>> el
[<String u'name'; value=u'Bob'>, <String u'name'; value=u'Biff'>]

If more than one Element is specified in *schema, an anonymous Dict is created to hold them.

>>> from flatland import Integer
>>> Points = Array.of(Integer.named('x'), Integer.named('y'))
>>> Points.member_schema
<class 'flatland.schema.containers.Dict'>
>>> el = Points([dict(x=1, y=2)])
>>> point = el[0]
>>> point['x']
<Integer u'x'; value=1>
>>> point['y']
<Integer u'y'; value=2>

set(iterable)

Assign the native and Unicode value.

Attempts to adapt the given iterable and assigns this element’s value and u attributes in tandem. Returns True if the adaptation was successful. See Element.set().

Set must be supplied a Python sequence or iterable:

>>> from flatland import Integer, List
>>> Numbers = List.of(Integer)
>>> nums = Numbers()
>>> nums.set([1, 2, 3, 4])
True
>>> nums.value
[1, 2, 3, 4]

set_default()

set() the element to the schema default.

append(value)

Append value to end.

If value is not an instance of member_schema, it will be wrapped in a new element of that type before appending.

extend(iterable)

Append iterable values to the end.

If values of iterable are not instances of member_schema, they will be wrapped in a new element of that type before extending.

insert(index, value)

Insert value at index.

If value is not an instance of member_schema, it will be wrapped in a new element of that type before inserting.

remove(value)

Remove member with value value.

If value is not an instance of member_schema, it will be wrapped in a new element of that type before searching for a matching element to remove.

index(value)

Return first index of value.

If value is not an instance of member_schema, it will be wrapped in a new element of that type before searching for a matching element in the sequence.

count(value)

Return number of occurrences of value.

If value is not an instance of member_schema, it will be wrapped in a new element of that type before searching for matching elements in the sequence.

class Mapping(value=Unspecified, **kw)

Bases: flatland.schema.containers.Container, dict

Base of mapping-like Containers.

field_schema = ()

Todo

doc field_schema

may_contain(key)

Return True if the element schema allows a field named key.

clear() → None. Remove all items from D.

popitem() → (k, v), remove and return some (key, value) pair as a

2-tuple; but raise KeyError if D is empty.

pop(k[, d]) → v, remove specified key and return the corresponding value.

If key is not found, d is returned if given, otherwise KeyError is raised

update(*dictish, **kwargs)

Update with keys from dict-like *dictish and **kwargs

setdefault(k[, d]) → D.get(k,d), also set D[k]=d if k not in D

get(k[, d]) → D[k] if k in D, else d. d defaults to None.

set(value)

Todo

doc set()

set_default()

set() the element to the schema default.

u

A string repr of the element.

value

The element as a regular Python dictionary.

is_empty

Mappings are never empty.

class Compound(value=Unspecified, **kw)

Bases: flatland.schema.containers.Mapping, flatland.schema.scalars.Scalar

A mapping container that acts like a scalar value.

Compound fields are dictionary-like fields that can assemble a u and value from their children, and can decompose a structured value passed to a set() into values for its children.

A simple example is a logical calendar date field composed of 3 separate Integer component fields, year, month and day. The Compound can wrap the 3 parts up into a single logical field that handles datetime.date values. Set a date on the logical field and its component fields will be set with year, month and day; alter the int value of the year component field and the logical field updates the date to match.

Compound is an abstract class. Subclasses must implement compose() and explode().

Composites run validation after their children.

compose()

Return a text, native tuple built from children’s state.

Returns:a 2-tuple of text representation, native value. These correspond to the serialize_element() and adapt_element() methods of Scalar objects.

For example, a compound date field may return a ‘-‘ delimited string of year, month and day digits and a datetime.date.

explode(value)

Given a compound value, assign values to children.

Parameters:value – a value to be adapted and exploded

For example, a compound date field may read attributes from a datetime.date value and set() them on child fields.

The decision to perform type checking on value is completely up to you and you may find you want different rules for different compound types.

serialize(value)

Not implemented for Compound types.

set(value)

Todo

doc set()

is_empty

True if all subfields are empty.

The Flatland Project

License

Copyright © The Flatland authors and contributors

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the “Software”), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED “AS IS”, WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

Authors & Contributors

Flatland was originally written by Jason Kirtland.

Contributors are:

• Dan Colish <dcolish@gmail.com>
• Jason Kirtland <jek@discorporate.us>
• Adam Lowry
• Dag Odenhall
• Michel Pelletier
• Ollie Rutherfurd
• Benjamin Stover
• Thomas Waldmann
• Scott Wilson

Portions derived from other open source works and are clearly marked.

History

Flatland is a Python implementation of techniques I’ve been using for form and web data processing for ages, in many different languages. It is an immediate conceptual descendant and re-write of “springy”, a closed-source library used internally at Virtuous, Inc. The Genshi filter support was donated to the Flatland project by Virtuous.

Documentation Todo List

Todo

doc descent_validators

(The original entry is located in /home/docs/checkouts/readthedocs.org/user_builds/flatland/checkouts/latest/flatland/schema/containers.py:docstring of flatland.schema.containers.Container.descent_validators, line 1.)

Todo

doc field_schema

(The original entry is located in /home/docs/checkouts/readthedocs.org/user_builds/flatland/checkouts/latest/flatland/schema/containers.py:docstring of flatland.schema.containers.Mapping.field_schema, line 1.)

Todo

doc set()

(The original entry is located in /home/docs/checkouts/readthedocs.org/user_builds/flatland/checkouts/latest/flatland/schema/containers.py:docstring of flatland.schema.containers.Mapping.set, line 1.)

Todo

doc set()

(The original entry is located in /home/docs/checkouts/readthedocs.org/user_builds/flatland/checkouts/latest/flatland/schema/compound.py:docstring of flatland.schema.compound.Compound.set, line 1.)

Todo

intro

(The original entry is located in /home/docs/checkouts/readthedocs.org/user_builds/flatland/checkouts/latest/docs/source/schema/dicts.rst, line 7.)

Todo

strict, duck, etc.

(The original entry is located in /home/docs/checkouts/readthedocs.org/user_builds/flatland/checkouts/latest/docs/source/schema/dicts.rst, line 14.)

Todo

doc of()

(The original entry is located in /home/docs/checkouts/readthedocs.org/user_builds/flatland/checkouts/latest/flatland/schema/containers.py:docstring of flatland.schema.containers.Dict.of, line 1.)

Todo

doc set()

(The original entry is located in /home/docs/checkouts/readthedocs.org/user_builds/flatland/checkouts/latest/flatland/schema/containers.py:docstring of flatland.schema.containers.Dict.set, line 1.)

Todo

FIXME UPDATE:

FieldSchemas are a bit like Python class definitions: they need be defined only once and don’t do much on their own. FieldSchema.create_element() produces Elements; closely related objects that hold and manipulate form data. Much like a Python class, a single FieldSchema may produce an unlimited number of Element instances.

(The original entry is located in /home/docs/checkouts/readthedocs.org/user_builds/flatland/checkouts/latest/docs/source/schema/schema.rst, line 20.)

Todo

FIXME UPDATE:

FieldSchema instances may be freely composed and shared among many containers.

(The original entry is located in /home/docs/checkouts/readthedocs.org/user_builds/flatland/checkouts/latest/docs/source/schema/schema.rst, line 36.)

Todo

FIXME UPDATE:

Elements can be supplied to template environments and used to great effect there: elements contain all of the information needed to display or redisplay a HTML form field, including errors specific to a field.

The u, x, xa and el() members are especially useful in templates and have shortened names to help preserve your sanity when used in markup.

(The original entry is located in /home/docs/checkouts/readthedocs.org/user_builds/flatland/checkouts/latest/docs/source/schema/schema.rst, line 50.)