result[:-1] means start from the end of the string and go one step backward

Accepting negative indices is a Python feature.

Why?

This is the way of doing it

I don't think convoluting the logic by introducing unecessary structures would be considered proper; unless you strongly suspected that you would in fact need to know what was pushed later on, and didn't want to have to make large changes later.

I would add len(self) for correctness.

But it is better to use the stack for more correct logic.