How can I simulate a “locked” file (one which has a write lock)

Question

I am trying to debug a problem where users occasionally have locked files which they try to open. The code appears to have correct exception handling but users are still report

Answer 1

I used LockFileEx function from the Windows API to write a unittest in Python. This worked well for me (shutil.copy() with a locked target fails).

import win32con
import win32file
import pywintypes

p = "yourfile.txt"
f = file(p, "w")
hfile = win32file._get_osfhandle(f.fileno())
flags = win32con.LOCKFILE_EXCLUSIVE_LOCK | win32con.LOCKFILE_FAIL_IMMEDIATELY

win32file.LockFileEx(hfile, flags, 0, 0xffff0000, pywintypes.OVERLAPPED())

See: https://msdn.microsoft.com/en-us/library/windows/desktop/aa365203%28v=vs.85%29.aspx