thirdparty: vendor attrs
The attrs package allows defining namedtuple-like classes with no weird
behavior and no runtime performance cost.
This patch vendors in attrs 17.2.0.
# no-check-commit
Differential Revision: https://phab.mercurial-scm.org/D867
"""
Commonly useful converters.
"""
from __future__ import absolute_import, division, print_function
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