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""" |
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Commonly useful converters. |
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""" |
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from __future__ import absolute_import, division, print_function |
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def optional(converter): |
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""" |
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A converter that allows an attribute to be optional. An optional attribute |
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is one which can be set to ``None``. |
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:param callable converter: the converter that is used for non-``None`` |
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values. |
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.. versionadded:: 17.1.0 |
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""" |
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def optional_converter(val): |
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if val is None: |
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return None |
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return converter(val) |
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return optional_converter |