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# SPDX-License-Identifier: MIT
"""
Commonly useful converters.
"""
import typing
from ._compat import _AnnotationExtractor
from ._make import NOTHING, 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.
: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)
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]
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 `attrs.Factory` is supported, however the ``takes_self`` option
is *not*.
:param callable factory: A callable that takes no 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 `attrs.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
def to_bool(val):
"""
Convert "boolean" strings (e.g., from env. vars.) to real booleans.
Values mapping to :code:`True`:
- :code:`True`
- :code:`"true"` / :code:`"t"`
- :code:`"yes"` / :code:`"y"`
- :code:`"on"`
- :code:`"1"`
- :code:`1`
Values mapping to :code:`False`:
- :code:`False`
- :code:`"false"` / :code:`"f"`
- :code:`"no"` / :code:`"n"`
- :code:`"off"`
- :code:`"0"`
- :code:`0`
:raises ValueError: for any other value.
.. versionadded:: 21.3.0
"""
if isinstance(val, str):
val = val.lower()
truthy = {True, "true", "t", "yes", "y", "on", "1", 1}
falsy = {False, "false", "f", "no", "n", "off", "0", 0}
try:
if val in truthy:
return True
if val in falsy:
return False
except TypeError:
# Raised when "val" is not hashable (e.g., lists)
pass
raise ValueError(f"Cannot convert value to bool: {val}")