Gimme some random passwords pwgen is a nice password generator utility. 
When you run it, it fills the terminal with a bunch of random passwords,
giving you many options to choose from and pick something you like,
for example:


lvk3U7cKJYkl pLBJ007977Qx b9xhj8NWPfWQ
pMgUJBUuXwpG OAAqf6Y9TXqc fJOyxoGYCRSQ
bpbwp6f2MxEH fUYTJUqg0ZMB GjVVEQxuer0k
oqTEvV1LmdJu si47MkHNRpAw 3GKV8NdGMvwf



Although there are ports of pwgen in multiple systems,
it's not so easy to find in Windows.
So I put together a simple Python script that's more portable,
as it can run in any system with Python.

I added some extra features I often want:


Skip characters that may be ambiguous, such as l1ioO0Z2I
Avoid doubled characters (slow down typing)


Here it goes:

#!/usr/bin/env python

from __future__ import print_function

import random
import string
import re

from argparse import ArgumentParser

terminal_width = 80
terminal_height = 25

default_length = 12

alphabet_default = string.ascii_letters + string.digits
alphabet_complex = alphabet_default + '`~!@#$%^&amp;*()_+-={}[];:&lt;&gt;?,./'
alphabet_easy = re.sub(r'[l1ioO0Z2I]', '', alphabet_default)

double_letter = re.compile(r'(.)\1')


def randomstring(alphabet, length=16):
    return ''.join(random.choice(alphabet) for _ in range(length))


def has_double_letter(word):
    return double_letter.search(word) is not None


def easy_to_type_randomstring(alphabet, length=16):
    while True:
        word = randomstring(alphabet, length)
        if not has_double_letter(word):
            return word


def pwgen(alphabet, easy, length=16):
    for _ in range(terminal_height - 3):
        for _ in range(terminal_width // (length + 1)):
            if easy:
                print(easy_to_type_randomstring(alphabet, length), end=' ')
            else:
                print(randomstring(alphabet, length), end=' ')
        print()


def main():
    parser = ArgumentParser(description='Generate random passwords')
    parser.add_argument('-a', '--alphabet',
                        help='override the default alphabet')
    parser.add_argument('--complex', action='store_true', default=False,
                        help='use a very complex default alphabet', dest='complex_')
    parser.add_argument('--easy', action='store_true', default=False,
                        help='use a simple default alphabet, without ambiguous or doubled characters')
    parser.add_argument('-l', '--length', type=int, default=default_length)
    args = parser.parse_args()

    alphabet = args.alphabet
    complex_ = args.complex_
    easy = args.easy
    length = args.length

    if alphabet is None:
        if complex_:
            alphabet = alphabet_complex
        elif easy:
            alphabet = alphabet_easy
        else:
            alphabet = alphabet_default
    elif len(alphabet) &lt; length:
        length = len(alphabet)

    pwgen(alphabet, easy, length)


if __name__ == '__main__':
    main()


How would you improve this? I'm looking for comments about all aspects of this code.

I know that the terminal_width = 80 and terminal_height = 25 variables don't really reflect what their names imply. It's not terribly important, and good enough for my purposes, but if there's a way to make the script detect the real terminal width and height without importing dependencies that reduce portability, that would be pretty awesome.
Looking at the following:

terminal_width = 80
terminal_height = 25

default_length = 12

alphabet_default = string.ascii_letters + string.digits
alphabet_complex = alphabet_default + '`~!@#$%^&amp;*()_+-={}[];:&lt;&gt;?,./'
alphabet_easy = re.sub(r'[l1ioO0Z2I]', '', alphabet_default)

double_letter = re.compile(r'(.)\1')


you never change them, so they are constants. Constants are written ALL CAPS in Python as a convention.



elif len(alphabet) &lt; length:
    length = len(alphabet)


Are you sure the user really wants what you are doing here? Maybe he wants a 20 character password using only the 10 digits, with this you are silently not doing what he expects.