Password Generation Script

#!/usr/bin/python3

# This is public domain software.  No warranty is implied.
# It may not be suitable for any purpose.

import os
import sys
import string
from math import log, ceil
import time
import random

def get_bits(n, generator = os.urandom):
  byte_count = (n+7)//8
  data = generator(byte_count)
  return int(''.join(['%02x' % x for x in data]), 16)

ALPHABET_32 = string.ascii_lowercase + '234567'
ALPHABET_62 = string.ascii_letters + string.digits
ALPHABET_84 = ALPHABET_62 + string.punctuation

ALPHABETS = [string.ascii_letters, ALPHABET_62, ALPHABET_84, ALPHABET_32]

def create_password(bits, alphabet = ALPHABET_62, generator = os.urandom):
  alphabet_size = len(alphabet)
  length = ceil(log(1<<bits) / log(alphabet_size))
  bits = ceil(log(alphabet_size**length) / log(2))
  seed = get_bits(bits+32, generator) # reduce bias by getting extra bits
  result = ''
  while len(result) < length:
    result += alphabet[seed % alphabet_size]
    seed //= alphabet_size
  return result

if __name__ == '__main__':
  args = sys.argv[1:]
  if len(args) > 0:
    assert(len(args) >= 2 and len(args) <= 4)
    alphabet = ALPHABET_62
    if len(args) < 3:
      args = [args[0], args[0], args[1]]
    elif len(args) >= 4:
      if args[2] == '84':
        alphabet = ALPHABET_84
    path = os.path.join(os.getenv('HOME'), 'Crypto', 'Passwords', args[2] + '.gpg')
    print(path)
    assert not os.path.exists(path)
    pw = create_password(80, alphabet, (args[0]+args[1]+args[2]).encode('utf8'))
    pipe = os.popen('gpg -e -r %s > "%s"' % (os.getenv('USER'), path), 'w')
    pipe.write('%s\n%s\n%s\n' % (args[1], args[0], pw))
    pipe.close()

  while True:
    print(create_password(80, random.choice(ALPHABETS)))
    time.sleep(2)