Watching a file another app is writing

[Gordon Airporte]

I'm trying to find a way to take a file that another program has opened 
and writes to periodically, open it simultaneously in Python, and 
automatically update some of my objects in Python when the file is 
written to.
I can open the file and manually readlines() from it to keep up to date, 
it's the automatic part I'm having trouble with. This is on Windows.