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# SPDX-License-Identifier: MIT
"""
Commonly useful converters.
"""
import typing
from ._compat import _AnnotationExtractor
from ._make import NOTHING, Converter, Factory, pipe
__all__ = [
"default_if_none",
"optional",
"pipe",
"to_bool",
]
def optional(converter):
"""
A converter that allows an attribute to be optional. An optional attribute
is one which can be set to `None`.
Type annotations will be inferred from the wrapped converter's, if it has
any.
Args:
converter (typing.Callable):
the converter that is used for non-`None` values.
.. versionadded:: 17.1.0
"""
if isinstance(converter, Converter):
def optional_converter(val, inst, field):
if val is None:
return None
return converter(val, inst, field)
else:
def optional_converter(val):
if val is None:
return None
return converter(val)
xtr = _AnnotationExtractor(converter)
t = xtr.get_first_param_type()
if t:
optional_converter.__annotations__["val"] = typing.Optional[t]
rt = xtr.get_return_type()
if rt:
optional_converter.__annotations__["return"] = typing.Optional[rt]
if isinstance(converter, Converter):
return Converter(optional_converter, takes_self=True, takes_field=True)
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*.
Args:
default:
Value to be used if `None` is passed. Passing an instance of
`attrs.Factory` is supported, however the ``takes_self`` option is
*not*.
factory (typing.Callable):
A callable that takes no parameters whose result is used if `None`
is passed.
Raises:
TypeError: If **neither** *default* or *factory* is passed.
TypeError: If **both** *default* and *factory* are passed.
ValueError:
If an instance of `attrs.Factory` is passed with
``takes_self=True``.
.. versionadded:: 18.2.0
"""
if default is NOTHING and factory is None:
msg = "Must pass either `default` or `factory`."
raise TypeError(msg)
if default is not NOTHING and factory is not None:
msg = "Must pass either `default` or `factory` but not both."
raise TypeError(msg)
if factory is not None:
default = Factory(factory)
if isinstance(default, Factory):
if default.takes_self:
msg = "`takes_self` is not supported by default_if_none."
raise ValueError(msg)
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
def to_bool(val):
"""
Convert "boolean" strings (for example, from environment variables) to real
booleans.
Values mapping to `True`:
- ``True``
- ``"true"`` / ``"t"``
- ``"yes"`` / ``"y"``
- ``"on"``
- ``"1"``
- ``1``
Values mapping to `False`:
- ``False``
- ``"false"`` / ``"f"``
- ``"no"`` / ``"n"``
- ``"off"``
- ``"0"``
- ``0``
Raises:
ValueError: For any other value.
.. versionadded:: 21.3.0
"""
if isinstance(val, str):
val = val.lower()
if val in (True, "true", "t", "yes", "y", "on", "1", 1):
return True
if val in (False, "false", "f", "no", "n", "off", "0", 0):
return False
msg = f"Cannot convert value to bool: {val!r}"
raise ValueError(msg)