Question

Getting two different modification time when calculated from different Python versions on Windows XP.

Python2.4

C:\Copy of elisp>c:\python24\python
Python 2.4.4 (#71, Oct 18 2006, 08:34:43) [MSC v.1310 32 bit (Intel)] on win32
Type "help", "copyright", "credits" or "license" for more information.
>>> import os
>>> os.path.getmtime("auto-complete-emacs-lisp.el")
1251684178
>>> ^Z

Python2.6

C:\Copy of elisp>C:\Python26\python
Python 2.6.4 (r264:75708, Oct 26 2009, 08:23:19) [MSC v.1500 32 bit (Intel)] on win32
Type "help", "copyright", "credits" or "license" for more information.
>>> import os
>>> os.path.getmtime("auto-complete-emacs-lisp.el")
1251687778.0
>>>

There is a difference of 3600 seconds reported by Python2.6 and Python2.4.

What is the reason of this strange behavior?

Answer 1

It’s a bug in Microsoft’s implementation of the C standard library. Python 2.4 used to use the stdlib fstat call to get file information, and hence could end up an hour out in locales that use DST.

In Python 2.5 and later, os.stat calls the direct Win32-only API to get file information when running on Windows, resulting in the correct output. See this thread for more.