Multiprocessing example, iterating over each line in a file.

multi.py

import multiprocessing
import StringIO

# function to be run on each line of file
def f(x):
    print x,

# Create mock file
mock_file = StringIO.StringIO()
for i in range(20):
    mock_file.write("{}\n".format(i))
mock_file.seek(0)

# run it!
pool = multiprocessing.Pool(processes=4)
pool.map(f, mock_file)

# Cleanup
mock_file.close()