if-else.md

Python by Example: If/Else

Conditionals let your program choose different paths based on data. Python uses indentation (spaces) to define blocks—no braces needed. Use if for the first condition, elif for additional ones, and else for the fallback. Indentation matters: use 4 spaces consistently.

What you'll learn:

• if, elif, and else
• Indentation rules
• Truthiness: empty lists and zero are falsy
• One-line conditional expressions

x = 10

if x > 10:
    print("greater than 10")
elif x == 10:
    print("exactly 10")
else:
    print("less than 10")

# One-line conditional expression
result = "even" if x % 2 == 0 else "odd"
print(result)

# Truthiness: empty sequences and zero are falsy
items = []
if not items:
    print("list is empty")

elif is short for "else if." The expression "even" if x % 2 == 0 else "odd" chooses one of two values. Empty lists ([]) and zero are "falsy"—if not items: is True when the list is empty.

To run this program:

$ python source/if-else.py
exactly 10
even
list is empty

Tip: Use 4 spaces for indentation. Never mix tabs and spaces—Python will complain. Most editors insert spaces when you press Tab.

Try it: Change x to 11 or 9 and see which branch runs.

Source: if-else.py

Next: Match