Python - Operator Precedence

Overview

Estimated time: 20–30 minutes

Operator precedence determines which operations are evaluated first in an expression. Understanding this avoids subtle bugs and improves code readability.

Learning Objectives

• Know Python’s operator precedence and associativity rules.
• Predict evaluation of complex expressions and parenthesize intentionally.
• Recognize short-circuit behavior for boolean operators.

Prerequisites

• Basic familiarity with Python operators and expressions

Quick Reference (highest → lowest)

Common subset: parentheses () → exponentiation ** (right-assoc) → unary + - ~ → multiply/divide * / // % → add/subtract + - → shifts << >> → bitwise & then ^ then | → comparisons < <= > >= == != is in → not → and → or → if-else expression → assignment (walrus :=)

Examples

print(2 + 3 * 4)          # 14, * before +
print((2 + 3) * 4)        # 20
print(2 ** 3 ** 2)        # 512, right-associative: 2 ** (3 ** 2)
print(-3 ** 2)            # -9, unary - after **; use (-3) ** 2 for 9
print(1 or 0 and 5)       # 1, and before or; also short-circuiting

# Short-circuiting returns operands, not coerced booleans
x = []
print(x or [42])          # [42]
print(x and [42])         # []

Expected Output:

14
20
512
-9
1
[42]
[]

Common Pitfalls

• Unary minus vs exponentiation: -3 ** 2 is -(3 ** 2), not (-3) ** 2.
• Chained comparisons: a < b < c is equivalent to a < b and b < c and evaluates b once.
• Boolean short-circuit values: and/or return operands, not True/False.
• Readability: when in doubt, add parentheses.

Best Practices

• Use parentheses generously to document intent.
• Avoid overly clever one-liners; split into intermediate variables.
• Prefer explicit if/else over nested ternaries for clarity.

Checks for Understanding

1. What is the value of 2 + 3 * 2 ** 2?
2. How does a or b choose which value to return?

Exercises

1. Rewrite a complex expression with parentheses to make evaluation order obvious.
2. Create examples showing the difference between -3 ** 2 and (-3) ** 2.