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