|
|
- """
- Commonly useful converters.
- """
-
- from __future__ import absolute_import, division, print_function
-
- from ._make import NOTHING, Factory
-
-
- def optional(converter):
- """
- A converter that allows an attribute to be optional. An optional attribute
- is one which can be set to ``None``.
-
- :param callable converter: the converter that is used for non-``None``
- values.
-
- .. versionadded:: 17.1.0
- """
-
- def optional_converter(val):
- if val is None:
- return None
- return converter(val)
-
- return optional_converter
-
-
- def default_if_none(default=NOTHING, factory=None):
- """
- A converter that allows to replace ``None`` values by *default* or the
- result of *factory*.
-
- :param default: Value to be used if ``None`` is passed. Passing an instance
- of :class:`attr.Factory` is supported, however the ``takes_self`` option
- is *not*.
- :param callable factory: A callable that takes not parameters whose result
- is used if ``None`` is passed.
-
- :raises TypeError: If **neither** *default* or *factory* is passed.
- :raises TypeError: If **both** *default* and *factory* are passed.
- :raises ValueError: If an instance of :class:`attr.Factory` is passed with
- ``takes_self=True``.
-
- .. versionadded:: 18.2.0
- """
- if default is NOTHING and factory is None:
- raise TypeError("Must pass either `default` or `factory`.")
-
- if default is not NOTHING and factory is not None:
- raise TypeError(
- "Must pass either `default` or `factory` but not both."
- )
-
- if factory is not None:
- default = Factory(factory)
-
- if isinstance(default, Factory):
- if default.takes_self:
- raise ValueError(
- "`takes_self` is not supported by default_if_none."
- )
-
- def default_if_none_converter(val):
- if val is not None:
- return val
-
- return default.factory()
-
- else:
-
- def default_if_none_converter(val):
- if val is not None:
- return val
-
- return default
-
- return default_if_none_converter
|
