The best function to use for this is os.path.getmtime(). Internally, this just uses os.stat(filename).st_mtime.
The datetime module is the best manipulating timestamps, so you can get the modification date as a datetime object like this:
import os
import datetime
def modification_date(filename):
t = os.path.getmtime(filename)
return datetime.datetime.fromtimestamp(t)
Usage example:
>>> d = modification_date('/var/log/syslog')
>>> print d
2009-10-06 10:50:01
>>> print repr(d)
datetime.datetime(2009, 10, 6, 10, 50, 1)