first_mention.py

from parse_bible import bible, books

word = input('Enter a word you wish to find the first occurrence of: ')

for book in books:
    for chapter_num, chapter in enumerate(bible[book]):
        for verse_num, verse in enumerate(chapter):
            if word in verse:
                print("First mention of {} is in {} {}:{}".format(word, book, chapter_num+1, verse_num+1))
                exit()