Python course / Foundations

Conditions and branching

Make a program choose, with if, elif and match, and combine conditions without tying them in knots. The traps here are quiet ones: floats that do not compare as you expect, an or that looks right and is not, None mistaken for zero.

comparisons
if and elif
and, or, not
truthiness
None vs falsy
match
nesting
walrus

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one value, several outcomes, in order

def fare(age, day):
    if age < 5:
        return 0.0
    if age < 16 or age >= 65:
        return 1.20
    if day in ("Saturday", "Sunday"):
        return 1.80
    return 2.40


for case in [(3, "Monday"), (12, "Monday"), (30, "Sunday"), (30, "Monday")]:
    print(case, "->", fare(*case))

(3, 'Monday') -> 0.0
(12, 'Monday') -> 1.2
(30, 'Sunday') -> 1.8
(30, 'Monday') -> 2.4

What you will learn

Run code only when a condition holds.
Pick one outcome from several, in the right order.
Combine conditions and control how they group.
Tell a missing value from a falsy one, and is from ==.
Choose a branch by comparing one value against several patterns.
Turn deep nesting into a flat chain, in an order that is safe.

The lessons in this module

Comparisons
Comparing text and numbers
if
else
elif
Comparing decimals
and, or, not
Truthiness
Empty collections
The or trap
None, == and is
Chained comparisons
in
not in
Conditional expressions
match
The capture trap
Matching shapes
Nested conditions
Flattening nested conditions
Assigning inside a condition
Module review: ticket desk

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