opening a file

[Tim Hanson]

Using linux and Python 2.6, learning how to work with files from a Windows 
oriented textbook:

This works:
infile=open('/foo/bar/prog/py_modules/this_is_a_test','r')

This doesn't:
infile=open('~/prog/py_modules/this_is_a_test','r')

Can't I work with files using Unix expressions?