#!/usr/bin/env python

import math
import hashlib

def H(data):
  if not data:
    return 0
  entropy = 0
  for x in range(len(data)):
    p_x = float(data.count(chr(x)))/len(data)
    if p_x > 0:
      entropy += - p_x*math.log(p_x, 2)
  return entropy


somerandomstring = 'some random data'
somerandomhash = hashlib.sha256(somerandomstring).digest()
somerandomhash2 = hashlib.sha256(somerandomhash).digest()

print "H(X) is the entroy function of X"
print "H('%s')=%s" % (somerandomstring, H(somerandomstring))
print "H(hash('%s'))=%s" % (somerandomstring,H(somerandomhash))