/usr/lib/python3/dist-packages/attr/converters.py is in python3-attr 17.4.0-2.
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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 | """
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
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