Enumerate hashes - thanks to Ken Shirriff

mine.py

#!/usr/bin/python
import hashlib, struct

# Mine genesis block
ver = 1
prev_block = "0000000000000000000000000000000000000000000000000000000000000000"
mrkl_root =  "4a5e1e4baab89f3a32518a88c31bc87f618f76673e2cc77ab2127b7afdeda33b"
time_ = 1231006505
bits = 0x1d00ffff

# https://en.bitcoin.it/wiki/Difficulty
exp = bits >> 24
mant = bits & 0xffffff
target_hexstr = '%064x' % (mant * (1<<(8*(exp - 3))))
target_str = target_hexstr.decode('hex')

nonce = 0
while nonce < (2**32):
    header = ( struct.pack("<L", ver) + prev_block.decode('hex')[::-1] +
          mrkl_root.decode('hex')[::-1] + struct.pack("<LLL", time_, bits, nonce))
    hash = hashlib.sha256(hashlib.sha256(header).digest()).digest()
    print nonce, hash[::-1].encode('hex')
    if hash[::-1] < target_str:
        print 'success'
        #break
    nonce += 1