Message 75722 - Python tracker

If you doesn't care to the time zone (UTC), use:
>>> datetime.datetime(1970, 1, 1) + datetime.timedelta(seconds=-86400)
datetime.datetime(1969, 12, 31, 0, 0)

This code is portable on Windows, Linux but also works with 
IronPython:
http://www.codeplex.com/IronPython/WorkItem/View.aspx?WorkItemId=7269