[issue22138] patch.object doesn't restore function defaults

[Clint Hepner]

New submission from Clint Hepner:

Following a patch, a function's __defaults__ attribute is reset to None.

    def foo(x=5):
        return x

    assert foo() == 5  # As expected
    with unittest.mock.patch.object(foo, '__defaults__', (10,)):
        assert foo() == 10  # As expected

    assert foo() == 5  # Fails
    assert foo.__defaults__ is None  # Succeeds

----------
components: Library (Lib)
messages: 224801
nosy: chepner
priority: normal
severity: normal
status: open
title: patch.object doesn't restore function defaults
type: behavior
versions: Python 3.4

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue22138>
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