view mercurial/thirdparty/attr/converters.py @ 49201:c29e79d11b01 stable

test-dirstate: actually test the append code path in dirstate v2 Apparently it's not sufficient to modify a file to force the dirstate write-out, so the append code path was untested. By removing a file instead of changing we're forcing append to happen.
author Arseniy Alekseyev <aalekseyev@janestreet.com>
date Tue, 17 May 2022 14:59:25 +0100
parents 765eb17a7eb8
children e1c586b9a43c
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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