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view mercurial/thirdparty/attr/converters.py @ 46413:ed43b6fa847e stable

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copyright: update to 2021 Differential Revision: https://phab.mercurial-scm.org/D9885
author Matt Harbison <matt_harbison@yahoo.com>
date Wed, 27 Jan 2021 00:54:57 -0500
parents 765eb17a7eb8
children e1c586b9a43c
line wrap: on
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"""
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