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.