File output of lists in Python 2.7 (Windows)

#====================
# Title: [TUTORIAL] File Output of a numbered list
# Description: Find the numbers in a range and output it to a file, along with
# the sum of those numbers.
# Author: Stosswalkinator
# Date: 7/15/2013
#====================

lag = []
str(lag.extend(range(0,100,5)))
str(lag.extend(range(0,100,7)))
f = open('C:\Users\user_name\My Documents\python.txt', 'w')
f.write(str(lag))
f.write(str(sum(lag)))
f.close()