[issue21859] Add Python implementation of FileIO

[STINNER Victor]

STINNER Victor added the comment:

> Slightly corrected docstrings (but for larger changes C and Python implementations should be changed consistently).

I reviewed pyio_fileio_9.patch. The main issue is that I don't understand how self._fd is set to None. In the C implemented, it's set to -1 even if closefd is False.

For comments on docstrings which also concern the C code, can you maybe open a new issue with a reference to this issue or maybe even a link to my review, if you don't want to modify them in this issue?

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue21859>
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