Pinging core devs on this and #4153. Also I fixed the networking problems with my Cygwin buildbot worker so it's actually producing meaningful results again, and this will fix a number of tests.

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@benjaminp

There seems to be an extra distutils change mixed in here.

See issue description

This PR is based on top of #4153 which needs to be merged before this issue can be fixed, as the fix relies on ctypes, and the ctypes module can't be built without #4153.

Thank you for looking at this issue, though #4153 is the one that really needs attention from a core dev.

The bpo was closed under bpo-45537 (Cygwin is unsupported).

This bug does not seem exist any longer. At least I could not replicate it with 3.9 on Cygwin 10.0.

$ uname -a
CYGWIN_NT-10.0-22631 xps-ne 3.5.4-1.x86_64 2024-08-25 16:52 UTC x86_64 Cygwin

$ python pyio-example.py
io from '/usr/lib/python3.9/_pyio.py'
Hello, world!

pyio-example.py :

import _pyio as io
with io.StringIO() as f:
    f.write("Hello, world!")
    f.seek(0)
    content = f.read()

print(f"io from '{io.__file__}'")
print(content)  # Output: Hello, world!