""" 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 `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 `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