Demo of how blockchain mining works, and why it gets harder and harder

mine_demo.py

""" 
    usage: python mine_demo.py ZEROES VALUE_TO_HASH

    Find a nonce that, when concatenated  with VALUE_TO_HASH, results in an 
    SHA256 hexdigest that starts with ZEROES number of zeroes.

    output: NONCE HASH

    Where NONCE is the solution that resulted in a HASH that the required 
    number of zeroes at the start.

    The more zeroes required, the harder it is to find the solution through 
    brute force.

    Example usage:

        $ python mine_demo.py 6 one-hundreds
        10849447 000000379be85754d2fca6c562c4a62b8546e7d2ec53eeaa0db656765bc4b662
"""

from hashlib import sha256
from sys import argv

def hash_value(val):

    """ Just turn any input into 256 bits of gibberish, AKA hash it.
    
        The important thing to know is that the output for a hash 
        will be unique for every input. 
    """
    
    return sha256(val.encode()).hexdigest()

def test_hash(hash_value, zcount):

    """ Test whether a string starts with zcount zero (0) characters. """

    while zcount >= 0:
        if hash_value[zcount] != "0":
            return False
        zcount -= 1
    return True

def test(nonce, something, zcount=0):

    """ Test whether the hash of a nonce plus some value (the previous block in 
        bitcoin mining) results in a hash that starts with zcount zero (0)
        characters. """
    
    result = hash_value(str(nonce) + something)

    if test_hash(result, zcount):
        return result
    
    return None


def main():
    zcount = int(argv[1]) - 1
    msg = str(argv[2])

    nonce = 0
    while True:
        solution = test(nonce, msg, zcount=zcount)
        if solution is not None:
            print nonce, solution
            break
        
        nonce += 1

if __name__ == "__main__":
    main()