Finds all anagrams for given words (Python 3).

anagrams.py

import math
import itertools

# Tested with dictionary from github.com/dwyl/english-words
WORDS_DICT_FILENAME = 'words_dictionary.json'

__dict = None
def get_valid_words():
    global __dict
    if __dict:
        return __dict
    with open(WORDS_DICT_FILENAME, 'r', encoding='utf-8') as dict_file:
        __dict = eval(dict_file.read())
        return __dict


def character_occurances(word):
    res = {}
    for c in word:
        res[c] = res[c] + 1 if c in res else 1
    return res


def are_anagrams(word1, word2):
    if len(word1) != len(word2):
        return False
    return character_occurances(word1) == character_occurances(word2)


def gen_anagrams(word, valid_words):
    word = word.lower()
    permutation_number = math.factorial(len(word))
    # If there are more possible character permutations of the input word,
    # than there are known valid words, then it is faster to simply check
    # every valid word for whether it's the input word's anagram.
    if permutation_number > len(valid_words):
        for dict_word in valid_words:
            if are_anagrams(dict_word, word):
                yield dict_word
        return
    # The word can have several occurances of one character, which means
    # some of its character permutations can be equal to others. (Swapping 'o's
    # in 'cowboy' doesn't change the word, but it is a valid permutation.)
    # We do not filter those non-unique permutations out, as it would require
    # storing all of them, which can take a lot of memory (factorial of
    # the word's length). Instead, we use a set to filter out repeated anagrams.
    anagrams = set()
    permutations = map(''.join, itertools.permutations(word))
    for possible_anagram in permutations:
        if possible_anagram in valid_words and not possible_anagram in anagrams:
            anagrams.add(possible_anagram)
            yield possible_anagram


if __name__ == '__main__':
    import sys

    words = sys.argv[1:]
    if not words:
        print('No words given in command line arguments.', end='\n\n')
        exit()

    print('Initializing word list...', end='\n\n')
    valid_words = get_valid_words()

    for word in words:
        word = word.lower()
        perm_number = math.factorial(len(word))
        print(f'Anagrams for "{word}" (out of {perm_number} options):')
        for anagram in gen_anagrams(word, valid_words):
            print('-', anagram)
        print()