* The extract process treats the file's timestamp in the zipfile as "local" time with "unknown" DST. It's theoretically possible that a DST change could cause the system to think that the file timestamp no longer matches the zip timestamp. Also, the resulting Unix-style timestamp for the extracted file may differ between systems with different timezones. This is an unfortunate side effect of the fact that the zip file format does not include timezone information or a UTC timestamp.

 

 * Cleanup on Windows doesn't work, because the .pyd's remain in use as long as some Python process using them is still running. An application that really wants to clean up on exit can presumably spawn another process to do something about it, but that kind of sucks, and doesn't account for the fact that another process might still be using the file anyway. (Michael Dubner suggested using ``HKEY_LOCAL_MACHINE\\SYSTEM\\CurrentControlSet\\Control\\Session Manager\\FileRenameOperations`` to fix the Windows problem, but unfortunately didn't give any details or sample code.) Sample code at http://aspn.activestate.com/ASPN/docs/ActivePython/2.2/PyWin32/win32api__MoveFileEx_meth.html, but in practice we really can't do this without requiring the PyWin32 extensions, which isn't such a great idea. So, the simple solution is to just avoid doing cleanups, and instead stick with a persistent cache directory.