$ python3 solver.py 
This is 'Bulls and cows' solver
Author: Vitaly Pavlenko, http://vk.com/vitalypavlenko
Date: Nov 11 2012

Think of some number of four digits.  All digits should be different.
For every question please answer two numbers: bulls and cows.
Example: if your secret number is 1234 and my question is 1453, you should answer '1 2'.

Question #1: 3762
0 1
Question #2: 5690
1 2
Question #3: 6594
0 2
Question #4: 5039
1 3
Your number is 5903.  It took me 5 steps to guess it.