Finding a file's directory address on a Mac

Question

I am working with a Macbook programming python. What I want to know is how I can access certain files using Python\'s file functions. A google search failed me.

For exam

Answer 1

f = open (r"/Users/USERNAME/Desktop/somedir/somefile.txt")

or even better

import os
f = open (os.path.expanduser("~/Desktop/somedir/somefile.txt"))

Because on bash (the default shell on Mac Os X) ~/ represents the user's home directory.