Selection: if / elif / else

Make your program choose what to do.

Selection lets a program make decisions. It runs some code only when a condition is true.

Comparing values

compare.py

print(5 > 3)
print(5 == 5)
print(5 != 4)
print(5 <= 2)

Output

True
True
True
False

How it works

Comparisons give a boolean (True or False).
> greater than, < less than, >= at least, <= at most.
== checks if two values are equal (two equals signs).
!= checks if they are not equal.

= is not === stores a value; == checks if two values are equal. Mixing them up is the most common beginner mistake.

if and else

age.py

age = int(input("Enter your age: "))
if age >= 18:
    print("You are an adult.")
else:
    print("You are a minor.")

Output

Enter your age: 16
You are a minor.

How it works

The condition after if is checked first.
If it is True, the indented lines under if run.
If it is False, the indented lines under else run instead.
The indentation — the spaces at the start of a line — tells Python which lines belong to each branch.

Adding more choices with elif

grade.py

score = int(input("Enter score: "))
if score >= 70:
    print("Grade: Distinction")
elif score >= 50:
    print("Grade: Merit")
elif score >= 40:
    print("Grade: Pass")
else:
    print("Grade: Fail")

Output

Enter score: 55
Grade: Merit

How it works

elif means 'else, if...' — it checks another condition only when the ones above were False.
Python tests each condition from top to bottom and stops at the first True one.
else at the end catches everything that did not match.

Combining conditions

logic.py

age = 15
member = True
if age >= 12 and member == True:
    print("Entry allowed")
if age < 12 or member == False:
    print("Please see staff")

Output

Entry allowed

How it works

and is True only when both conditions are true.
or is True when at least one condition is true.
You can write member instead of member == True, since member is already a boolean.

The patternif checks a condition; elif adds more conditions; else is the fallback when nothing matched.

What you have learned

Comparisons (>, <, >=, <=, ==, !=) give a boolean.
if runs code when its condition is True.
elif adds extra conditions, checked in order.
else runs when nothing above matched.
Combine conditions with and / or.
Indentation decides which lines belong to each branch.