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bpo-28459: Fix _pyio on Cygwin where the msvcrt module is not built #14013

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bpo-28459: Fix _pyio on Cygwin where the msvcrt module is not built #14013

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bpo-4032: Cygwin: Add .dll.a to UnixCCompiler for searching libraries
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ma8ma Oct 27, 2017
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bpo-28459: Fix _pyio on Cygwin where the msvcrt module is not built.
embray Jun 12, 2019
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bpo-28459: Fix _pyio on Cygwin where the msvcrt module is not built. 
Instead use ctypes to access the setmode function provided by Cygwin.
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@embray
embray committed Jun 12, 2019
commit 07f3c0dbb748e3add71b6e3569abe34fed388aa3
7 changes: 6 additions & 1 deletion Lib/_pyio.py
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Expand Up @@ -10,8 +10,13 @@
import sys
# Import _thread instead of threading to reduce startup cost
from _thread import allocate_lock as Lock
if sys.platform in {'win32', 'cygwin'}:
if sys.platform == 'win32':
from msvcrt import setmode as _setmode
elif sys.platform == 'cygwin':
import ctypes

@benjaminp benjaminp Sep 11, 2019

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We should avoid ctypes in the io module. There probably should cygwin equivalent for msvcrt instead.

@embray embray Sep 18, 2019

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@benjaminp This is the _pyio module used primarily only in testing. There is no "cygwin equivalent for msvcrt"--why should there be? The closest I can think of is my own PyCygwin package, and it's not part of the standard lib, though I'd be willing to make it so; I'm hardly interested in fighting for a new stdlib package just to fix one bug though.

As was discussed on the issue it would be possible to expose Cygwin's setmode() as os.setmode() but it could be confusing since it does not function the same the FreeBSD setmode().

_cygwin1 = ctypes.CDLL('cygwin1.dll')
def _setmode(fd, mode):
return _cygwin1._setmode(ctypes.c_int(fd), ctypes.c_int(mode))
else:
_setmode = None

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