view mercurial/thirdparty/attr/converters.py @ 35871:49ea1ba15ffd

wireprotoserver: make response handling attributes private

The send* methods are specific to sshserver and aren't part of the
common protocol interface. So rename them accordingly.

The handlers dict is also specific to sshserver and is related to
these methods. So give it the same treatment.

Differential Revision: https://phab.mercurial-scm.org/D1989

"""
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