Find a word that consists of certian letters in dictionary (a.k.a. 4 Pics 1 Word helper)

findword.py

#!/usr/bin/env python3

import argparse
import collections
import re

parser = argparse.ArgumentParser(
        description='Find a word consisting of certain letters in dictionary'
        )
parser.add_argument('letters',
        help="letters to choose from"
        )
parser.add_argument('-l', '--length',
        help="length of the word",
        type=int
        )
parser.add_argument('-d', '--dictionary',
        help="path to dictionary, default %(default)s",
        default="/usr/share/dict/words"
        )
parser.add_argument('-m', '--mask',
        help="regular expression to mask found words, eg. '...e.s'"
        )

args = parser.parse_args()
chars = collections.defaultdict(int)
for ch in args.letters.lower():
    chars[ch] += 1
if args.mask:
    mask = re.compile(args.mask, re.I)

with open(args.dictionary, 'r') as inf:
    for word in (w.strip() for w in inf):
        if ((args.length and len(word) != args.length) or
            (args.mask and not mask.match(word))):
            continue
        my_chars = dict(chars)
        for ch in word.lower():
            if ch in my_chars and my_chars[ch]>0:
                my_chars[ch] -= 1
            else:
                break
        else:
            print(word)