Find largest subset of words with unique letters

from itertools import islice

def load_words(filepath):
    """Loads words from the word list into a list."""

    with open(filepath, "r") as fp:
        return fp.read().splitlines()

def remove_words_with_repeat_letters(words):
    """Removes words with duplicate letters and returns the filtered list."""

    return [word for word in words if len(set(word)) == len(word)]

def max_subset_without_repeat_letters(wordsets, disallowed_letters=set(),
                                        index=-1, depth=0, hist=[]):
    """Given an index, find the maximum number of words after the last word which
    can be added to a pre-existing subset, without repeating any letters in the
    subset. Returns the largest possible amount of words that can be added to
    the subset.
    """

    # Print progress
    if depth == 1:
        print(index, end=" ")

    # Iterate through all the words that come after index
    for i in range(index + 1, len(wordsets)):
        word, wordset = wordsets[i]

        # Check that the word does not contain previous letters
        if disallowed_letters.isdisjoint(wordset):
            new_hist = hist + [word]
            max_subset_without_repeat_letters(wordsets, disallowed_letters |
                                        wordset, i, depth + 1, new_hist)
            if len(new_hist) >= 5:
                print("\n\n" + " ".join(new_hist) + "\n") # TODO: Save this

if __name__ == "__main__":
    words_path = "path_to_word_list_here"

    words = load_words(words_path)

    # Remove words with duplicate letters
    words = remove_words_with_repeat_letters(words)

    # import random
    # words = random.sample(words, 3000)

    # Pre-compute sets of words for performance.
    wordsets = tuple([(word, set(word)) for word in words])

    output = max_subset_without_repeat_letters(wordsets)