PRNG - creates no repeated numbers

codegen.py

import random
import os
import time
import json

def calculateSeed():
	return reduce(lambda x,y: x+y, map(int, list(str(11*((int(time.time()) << os.getpid()) >> int(time.time()/400000))/7))))

class CodeGen(object):

	def __init__(self):
		'''Hash Like Pseudo Random Number Generator'''
		self.dbfilename = 'dbrandom.json'
		fp = open(self.dbfilename)
		seednum = calculateSeed()
		random.seed(seednum)
		print 'initialized with seed:', seednum
		try:
			self.usedkeys = json.load(fp)
		except Exception:
			self.usedkeys = list()
		fp.close()
		self.nbytes = 5
		self.maxnum = 4

		#cantidad de numeros a generar
		self.nnum = 300
		
	def __hash(self, n, maxnum):
		num = random.randint(0, maxnum)
		s = list('qwertypsdfghjklzxcvbnm')
		sn = list('1234567890')
		random.shuffle(s)
		random.shuffle(sn)
		s = s[len(s)//2:] + s[:len(s)//2]
		j = random.sample(s, n-num) + random.sample(sn, num)
		for _ in range(3):
			random.shuffle(j)
		result = j[n//2:]+j[:n//2]
		random.shuffle(result)
		return ''.join(result)[::-1]

	def flush(self):
		fp = open(self.dbfilename, 'w')
		json.dump(self.usedkeys, fp)
		fp.close()

	def gen(self):
		try:
			for _ in xrange(self.nnum):
				code = self.hash(self.nbytes, self.maxnum)
				while code in self.usedkeys:
					code = self.__hash(self.nbytes, self.maxnum)
				self.usedkeys.append(code)
		except Exception:
			self.flush()

	def get_winner(self):
		print random.choice(self.usedkeys)