145 lines
3.5 KiB
Python
145 lines
3.5 KiB
Python
# SPDX-License-Identifier: MIT
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"""
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Commonly useful converters.
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"""
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import typing
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from ._compat import _AnnotationExtractor
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from ._make import NOTHING, Factory, pipe
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__all__ = [
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"default_if_none",
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"optional",
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"pipe",
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"to_bool",
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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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Type annotations will be inferred from the wrapped converter's, if it
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has any.
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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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xtr = _AnnotationExtractor(converter)
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t = xtr.get_first_param_type()
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if t:
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optional_converter.__annotations__["val"] = typing.Optional[t]
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rt = xtr.get_return_type()
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if rt:
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optional_converter.__annotations__["return"] = typing.Optional[rt]
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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 `attrs.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 no 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 `attrs.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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def to_bool(val):
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"""
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Convert "boolean" strings (e.g., from env. vars.) to real booleans.
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Values mapping to :code:`True`:
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- :code:`True`
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- :code:`"true"` / :code:`"t"`
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- :code:`"yes"` / :code:`"y"`
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- :code:`"on"`
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- :code:`"1"`
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- :code:`1`
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Values mapping to :code:`False`:
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- :code:`False`
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- :code:`"false"` / :code:`"f"`
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- :code:`"no"` / :code:`"n"`
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- :code:`"off"`
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- :code:`"0"`
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- :code:`0`
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:raises ValueError: for any other value.
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.. versionadded:: 21.3.0
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"""
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if isinstance(val, str):
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val = val.lower()
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truthy = {True, "true", "t", "yes", "y", "on", "1", 1}
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falsy = {False, "false", "f", "no", "n", "off", "0", 0}
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try:
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if val in truthy:
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return True
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if val in falsy:
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return False
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except TypeError:
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# Raised when "val" is not hashable (e.g., lists)
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pass
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raise ValueError("Cannot convert value to bool: {}".format(val))
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