Python helps you play Letterpress

letterpress.py

"""
Python helps you play `Letterpress <http://www.atebits.com/letterpress/>`_.

Requires `NLTK library <http://nltk.org/>`_ and cmudict corpus.
You can install the latter by executing the following two lines in Python shell:

>>> import nltk
>>> nltk.download()

I'd consider it cheating, though!
"""
import re
from collections import Counter
from nltk.corpus import cmudict

WORDS = [(word.lower(), Counter(word.lower()))
         for word in cmudict.words()
         if len(word) >= 3 and re.match('^[a-zA-Z]+$', word)]

# Weight of a white (neutral) letter
WHITE_WEIGHT = 1.0
# Weight of a light red (opposing player) letter
RED_WEIGHT = 1.9
# Blue (your) and dark red (protected) fields have weight 0

def hint(red, white, other):
    """Given light red, white and other letters on a board as strings,
    returns five words giving the most points."""
    target_red = Counter(red)
    target_white = Counter(white)
    target_all = Counter(red + white + other)
    def fit(word):
        result = 0
        for letter, count in word[1].items():
            target_all_count = target_all[letter]
            if count > target_all_count:
                return -1
            result += WHITE_WEIGHT * min(target_white[letter], count)
            result += RED_WEIGHT * min(target_red[letter], count)
            
        return result
        
    return sorted(WORDS, key=fit, reverse=True)[:5]

Noticed WHITE_WEIGHT on line 38 was misspelled ;)