Eryk Sun <[email protected]> added the comment:
I was able to reproduce this problem in 3.6 in Windows 10 (1709), but only for
code paths that call WriteFile, i.e. os.write and legacy standard I/O mode.
Writing to the console will block if there's an active text selection. The
operation completes once the user copies the selection to the clipboard (e.g.
by pressing enter). In the case of WriteFile, when the blocked call finally
completes, the console mistakenly returns the number of internally written
UTF-16 bytes.
This bug is not present with WriteConsoleA, which means there's a simple
workaround. _Py_write could detect a console handle and call WriteConsoleA
instead of _write.
The following test executes a write on a separate thread, after a timed delay
that allows selecting text beforehand. Text can be selected via Ctrl+A,
Shift+Up, or the mouse (the latter requires quick-edit mode or toggling mark
mode).
import os
import sys
import ctypes
import msvcrt
import threading
kernel32 = ctypes.WinDLL('kernel32', use_last_error=True)
fd_stdout = sys.stdout.fileno()
h_stdout = msvcrt.get_osfhandle(fd_stdout)
n = ctypes.c_ulong()
def test_write():
n.value = os.write(fd_stdout, b'spam\r\n')
def test_WriteFile():
kernel32.WriteFile(h_stdout, b'spam\r\n', 6, ctypes.byref(n), None)
def test_WriteConsoleA():
kernel32.WriteConsoleA(h_stdout, b'spam\r\n', 6, ctypes.byref(n), None)
For example, given manual text selection after starting the timer:
>>> threading.Timer(5, test_write).start()
>>> spam
>>> n
c_ulong(12)
>>> threading.Timer(5, test_WriteFile).start()
>>> spam
>>> n
c_ulong(12)
>>> threading.Timer(5, test_WriteConsoleA).start()
>>> spam
>>> n
c_ulong(6)
This test could be completely automated by combining SendInput (to set the
session control-key state), GetConsoleWindow, and PostMessageW (WM_KEYDOWN,
WM_KEYUP).
----------
versions: +Python 3.6
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<https://bugs.python.org/issue32245>
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