xkcd style password generator

xkcdpass.py

#!/usr/bin/env python
"""Generate a password in similar vein to XKCD 936"""
from __future__ import print_function, unicode_literals

import random
import string


class XKCDPasswordGenerator:
    """Generate a password in similar vein to XKCD 936"""

    def __init__(self, dictionary_file='/usr/share/dict/words'):
        self.dictionary = get_dict(dictionary_file)

    def get_dictword(self, length):
        """Return a random dictionary word of required length"""
        return random.choice(list(word.strip() for word in self.dictionary if len(word) > length))

    def genpass(self, words, digits):
        """Generate a random XKCD 936 password"""
        wordcount, wordlength = words

        padding = random.choice(string.punctuation) * 2
        separator = random.choice(string.punctuation)

        pwparts = [padding, get_digits(digits), separator]

        for i in range(wordcount):
            if i % 2 == 0:
                case = str.lower
            else:
                case = str.upper

            pwparts.append(case(self.get_dictword(wordlength)))
            pwparts.append(separator)

        pwparts.append(get_digits(digits))
        pwparts.append(padding)

        return ''.join(map(str, pwparts))


def get_digits(digits):
    """Return a random number with required number of digits"""
    return random.randint(10 ** (digits - 1), (10 ** digits) - 1)


def get_dict(filename='/usr/share/dict/words'):
    """Get sanitized words from a dictionary file"""
    words = []

    with open(filename) as dictfile:
        for word in dictfile:
            word = word.strip()
            if all(c in string.ascii_letters for c in word):
                words.append(word)

    return words


def main():
    """Main entry point"""
    import argparse

    parser = argparse.ArgumentParser()
    parser.add_argument('-w', '--words', help='number of words', type=int, default=3)
    parser.add_argument('-W', '--word-length', help='minimum word length', type=int, default=4)
    parser.add_argument('-d', '--digits', help='number of digits', type=int, default=2)
    parser.add_argument('-n', '--num-passwords', help='number of passwords to generate', type=int, default=1)
    args = parser.parse_args()

    generator = XKCDPasswordGenerator()
    for _ in range(args.num_passwords):
        print(generator.genpass((args.words, args.word_length), args.digits))


if __name__ == '__main__':
    main()