Create a random string/password

random_pw.py

#!/usr/bin/env python3
from __future__ import print_function
import random
import math
import sys
import argparse

#: alphabet of 2**6 letters
ALPHABET_64 = "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ+="


def make_pw(length=32, alphabet=ALPHABET_64, rng=None):
    rng = rng or random.SystemRandom()
    bits = math.log(len(alphabet), 2)
    if int(bits) != bits:
        print('Length of alphabet is not a power of 2, may bias selection', file=sys.stderr)
    bits = int(bits)
    letters = []
    while len(letters) < length:
        index = rng.getrandbits(bits)
        try:
            letters.append(alphabet[index])
        except IndexError:
            continue
    return ''.join(letters)


if __name__ == "__main__":
    CLI = argparse.ArgumentParser('Random Password generator')
    CLI.add_argument(
        '-l',
        '--length',
        help='number of characters is password',
        default=128,
        type=int,
    )
    CLI.add_argument(
        '-a',
        '--alphabet',
        help='sequence of characters to draw from',
        default=ALPHABET_64,
    )
    options = CLI.parse_args()
    print(make_pw(length=options.length, alphabet=options.alphabet))