A ladder of questions

A cinema has more than two prices: children under 5 pay nothing, children under 13 pay 50, adults pay 100. Two paths are not enough.

So you add else-if lines, and Python spells that elif. The computer asks the questions from the top. The moment one answer is true, it runs that path and skips the rest of the ladder. The else at the bottom catches everyone nobody else caught.

The first yes wins, and the rest of the ladder is skipped.

In code

if age < 5:
    price = 0
elif age < 13:
    price = 50
else:
    price = 100

Ticket price for a 30-year-old

age < 5 ?

age < 13 ?

age < 60 ?

else

question

age: 30

Is 30 below 5? No, so this path is skipped and the computer moves down.

Move 1 of 4

Mind the order

Because the first yes wins, the order of the questions matters. Say you grade marks like this: ask if the score is at least 50 first, and then if it is at least 75.

A score of 90 is at least 50, so the first path runs and the computer never gets to the second question. Put the strictest question first, and then work down to the loosest. Think about the ladder from the top rung.

Strictest question first, or the later ones never get a turn.

In code

if score >= 75:
    grade = "B"
elif score >= 50:
    grade = "C"