Conditions: if, elif, else

A program sometimes reaches a fork: if the input is like this do one thing, otherwise another. if does that. Next to if you write a question whose answer is either True or False.

1def solve(key):
2    if key > 100:
3        return "big"
4    elif key > 10:
5        return "medium"
6    else:
7        return "small"

The questions are asked top to bottom and the first true one runs; the rest are skipped. elif means "otherwise, is this true?" and else means "if none of them".

The tools for asking: == is it equal, != is it different, < > <= >= smaller or larger. % gives the remainder of a division: 7 % 2 is 1, 8 % 2 is 0. That is how you tell whether a number is even.

Tasks