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

classmethod 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

classmethod 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.

classmethod 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)])
>>> el
[{u'y': <Integer u'y'; value=2>, u'x': <Integer u'x'; value=1>}]

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.