Hangman game not working help!

hey my assignment is to create a hangman game by calling the topics from a text file: below is the code and the text file
The Problem: when i type in a letter its supposed to appear at the spot where the initial letter and replace the "_" but it doesnt work
I know the program is not finished yet but i want to get this problem out of the way first
thanks already for any help
txt file:
movies, the bourne ultimatum, star wars, batman the dark knight rises
food,lasagna, spaghetti, shrimp
books, the alchemist, the count of monte cristo, shogun