Issue #24881: Fixed setting binary mode in Python implementation of FileIO

on Windows and Cygwin.  Patch from Akira Li.

Lib/_pyio.py

@@ -8,12 +8,13 @@ import codecs
 import errno
 import array
 import stat
+import sys
 # Import _thread instead of threading to reduce startup cost
 try:
     from _thread import allocate_lock as Lock
 except ImportError:
     from _dummy_thread import allocate_lock as Lock
-if os.name == 'win32':
+if sys.platform in {'win32', 'cygwin'}:
     from msvcrt import setmode as _setmode
 else:
     _setmode = None

Misc/NEWS

@@ -79,6 +79,9 @@ Core and Builtins
 Library
 -------
 
+- Issue #24881: Fixed setting binary mode in Python implementation of FileIO
+  on Windows and Cygwin.  Patch from Akira Li.
+
 - Issue #21112: Fix regression in unittest.expectedFailure on subclasses.
   Patch from Berker Peksag.