Simple entropy calculation of a string

getStringEntropy.py

#!/usr/bin/python
"""
Simple entropy calculation of a string
"""
from __future__ import division
from math import log
from collections import Counter

def get_entropy(s):
    return -sum(i/len(s) * log(i/len(s),2) for i in Counter(s).values())

def main():
    """ main function """
    mys = str(raw_input('Please enter a string: '))
    print('Entropy of string is: ' + str(get_entropy(mys)))

if __name__ == "__main__":
    main()