[issue20440] Use Py_REPLACE/Py_XREPLACE macros

[Serhiy Storchaka]

Serhiy Storchaka added the comment:

> Unless some known bugs are being fixed, this should be 3.4 only.

For example here is a bug very similar to a bug fixed in issue16447.

class Nasty(str):
    def __del__(self):
        C.__qualname__ = "other"

class C:
    pass

C.__qualname__ = Nasty("abc")
C.__qualname__ = "normal"
C.__qualname__ = "normal"

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue20440>
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