from string import letters

def frequent_words(filename, n):
    wordlist = filter(len, [filter(lambda chr: chr in letters, word.lower()) for word in open(filename).read().split()])
    counts = dict((word, wordlist.count(word)) for word in wordlist)
    return [(word, counts[word]) for word in sorted(counts, key=lambda word: counts[word], reverse=True)][:n]