A function finding suitable nonce for encryption to guarantee certain number of leading zeros (here:8) in the cipher text (mimicking bitcoin mining)

bitcoin_mine.py

import hashlib
import random
import itertools

alphabetString = "abcdefghijklmnopqrstuvwxyz"

def doubleSHA256( plainText ):
	firstEncryption = hashlib.sha256()
	secondEncryption = hashlib.sha256()
	firstEncryption.update(plainText)
	secondEncryption.update(firstEncryption.digest())
	return secondEncryption.hexdigest()

def createHashWithLeadingZeros (plainText, numberOfZeros):
	nonceSize = 0
	enoughDifficulty = False
	composedMessage = None
	while enoughDifficulty is False:
		for nonce in itertools.imap(''.join, itertools.product(alphabetString, repeat=nonceSize)):
			doubleHash = doubleSHA256(plainText + nonce)
			if getNumberOfLeadingZeros(doubleHash) >= numberOfZeros:
				enoughDifficulty = True
				composedMessage = plainText + nonce
		nonceSize = nonceSize + 1
	return composedMessage

def getNumberOfLeadingZeros(word):
	return len(word) - len(word.lstrip('0'))

message = "aSampleTransactionToMine"
print createHashWithLeadingZeros(message, 8)