When is not a good time to use python generators?

This is rather the inverse of What can you use Python generator functions for?: python generators, generator expressions, and the itertools module are some of my favorite features of python these days. They’re especially useful when setting up chains of operations to perform on a big pile of data–I often use them when processing DSV files.

Pygame Window not Responding after few seconds

The below code makes the window not respond when started.. I wanted to make hangman game and I got the logic done and I was just trying to make the window pop up and its not responding. Also when I run the program, when I type in the letter and type another one then it erases the previous letter a writes the new letter with the underscores. How can I make it so that it keeps the previous letter and prints it with the new letter?