sentences = ['where are you now', 'here i am', 'can you do it', 'yes i can',
    'but can i do it', 'no you cant', 'do you feel good', 'yes i do',
    'why are you here', 'i dont know', 'i think i know why',
    'you dont think', 'yes i do', 'no you dont', 'i dont think you think',
    'i feel good', 'but i am good', 'i cant do it now', 'yes you can',
    'but i cant', 'where do you think i am']
for w in common_words:
    common_words_dict[w] = 0
for sentence in sentences:
    sentence_words = sentence.split(' ')
for word in sentence_words:
    if word in common_words_dict:
        common_words_dict[word] = common_words_dict[word] + 1
sorted_word_dict = sorted(list(common_words_dict.items()), key=operator.itemgetter(1)
    )
print(sorted_word_dict[::-1][:20])
Finding the "best" combination for a set