One is to write an if/elif/else chain of expressions ... the most familiar and idiomatic way to do this in Python. You cannot match against variable contents through indexing.

You can do explicit variable declarations in Python. But only the most diligent ... you’re not finished when you’ve checked where else it appears in the main file. In the second line you ...

The familiar formatted string, or f-string, feature in Python provides a convenient way to print variables as part of ... output.append(str(item).upper()) else: output.append(item) return ...

Post a runnable example that demonstrates the unwanted behavior. There are a number of different ways to cause that sort of thing in Python.