If Statements

Use if statements to run code only when a condition is true. The elif and else clauses are optional.

Syntax

if condition:
    # run if condition is true
elif another_condition:
    # run if previous conditions were false
else:
    # run if all conditions were false

Example

x = 10

if x < 0:
    print("Negative")
elif x % 2 != 0:
    print("Positive and odd")
else:
    print("Even or zero")

Truthiness

In a boolean context, these values are considered false:

• 0, 0.0

• None

• empty strings, lists, tuples, dicts, and sets

Everything else is considered true. The most Pythonic way to test a value is:

if x:
    print("x is truthy")

Avoid:

if x is True:
    ...

Common Pitfalls

• Forgetting the colon : after the condition.

• Missing indentation inside the block.

• Comparing directly to True or False unnecessarily.

Practice

1. Write a program that prints "adult" if age >= 18, otherwise "minor".

2. Extend it to print "senior" if age >= 65.

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