Quick script for getting entropy values for files

entropy.py

#!/usr/bin/python

import math, string, sys

def range_bytes (): return range(256)
def range_printable(): return (ord(c) for c in string.printable)
def H(data, iterator=range_bytes):
    if not data:
        return 0
    entropy = 0
    for x in iterator():
        p_x = float(data.count(chr(x)))/len(data)
        if p_x > 0:
            entropy += - p_x*math.log(p_x, 2)
    return entropy

if __name__ == '__main__':
    if len(sys.argv) == 1:
        print H(sys.stdin.read())
    else:
        for arg in sys.argv[1:]:
            e = H(open(arg, "rb").read())
            print "%s: %1.4f" % (arg, e)