Changing letters in a string dependant on case in python : <p>I'm a beginner at Python and I'm trying to self-teach. There's a task where I need to create a program that takes a string from the user and changes all uppercase letters to 'U' and all lowercase letters to 'l'.</p>

<p>I'm completely stuck with this, how is it possible to do this? From searching I've found about regular expressions, however this hasn't been covered yet and so I'm unsure that I'd be expected to use them.</p>
