7.11 Conditional (Ternary) Operator

Syntax

What Is It?

A one-line if/else that produces a value rather than executing a statement block: value_if_true if condition else value_if_false.

Why Is It Used?

For simple two-way choices, it’s more compact than a full if/else block.

status = "adult" if age >= 18 else "minor"
# equivalent to:
# if age >= 18:
#     status = "adult"
# else:
#     status = "minor"

Examples

>>> age = 20
>>> status = "adult" if age >= 18 else "minor"
>>> status
'adult'

Nested Ternary

Chaining ternaries handles more than two outcomes, but readability drops fast past one level of nesting — prefer a full if/elif/else for anything more complex than this.

>>> score = 75
>>> grade = "A" if score >= 90 else "B" if score >= 70 else "C"
>>> grade
'B'

Quick Interview Answer

“The conditional expression value_if_true if condition else value_if_false is Python’s ternary operator — it produces a value rather than executing a statement block, unlike a full if/else. It’s ideal for simple two-way choices assigned to a variable; chaining it for more than two outcomes technically works but readability drops fast, and a full if/elif/else block becomes the better choice past one level of nesting.”

Common Mistakes

• Nesting ternaries two or more levels deep — technically valid, but forces a reader to mentally trace multiple branches on one line.
• Using a ternary purely to save lines when the condition or branches are already complex expressions — readability should win over compactness here (see 7.17 Best Practices).