New submission from benrg <benrud...@gmail.com>:
On Windows, `mmap.mmap(f.fileno(), ...)` has the undocumented side effect of
setting f's file pointer to 0.
The responsible code in mmapmodule is this:
/* Win9x appears to need us seeked to zero */
lseek(fileno, 0, SEEK_SET);
Win9x is no longer supported, and I'm quite sure that NT doesn't have whatever
problem they were trying to fix. I think this code should be deleted, and a
regression test added to verify that mmap leaves the file pointer alone on all
platforms.
(mmap also maintains its own file pointer, the `pos` field of `mmap_object`,
which is initially set to zero. This issue is about the kernel file pointer,
not mmap's pointer.)
----------
components: IO, Library (Lib), Windows
messages: 414039
nosy: benrg, paul.moore, steve.dower, tim.golden, zach.ware
priority: normal
severity: normal
status: open
title: mmap constructor resets the file pointer on Windows
type: behavior
versions: Python 3.10, Python 3.11, Python 3.7, Python 3.8, Python 3.9
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Python tracker <rep...@bugs.python.org>
<https://bugs.python.org/issue46858>
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