1.8 Python Operators: Don't Let Them Trick You!

 

What is Operator Precedence?

Operator precedence in Python, as in most programming languages, defines the order in which operations are performed when multiple operators appear in an expression. It's like following a specific order of operations in mathematics.

How Does it Work?

Python has a predefined hierarchy of operators. Operators with higher precedence are evaluated before those with lower precedence. For instance, multiplication and division have higher precedence than addition and subtraction.

Example:

Python

result = 2 + 3 * 4

In this expression, the multiplication (3 * 4) is performed first due to its higher precedence, resulting in 12. Then, 2 is added to 12, giving 14 as the final result.

Operator Associativity

When two operators have the same precedence, their associativity determines the order of evaluation. Most operators in Python are left-associative, meaning they are evaluated from left to right. However, the exponentiation operator (**) is right-associative.

Example:

Python

result = 2 ** 3 ** 2

Here, the exponentiation is performed from right to left, so it's equivalent to 2 ** (3 ** 2), resulting in 2^9, which is 512.

The Precedence Table

To avoid confusion, it's helpful to refer to a precedence table. While the exact order might vary slightly between Python versions, the general hierarchy is as follows (from highest to lowest precedence):

1. Parentheses: Used to explicitly control the order of operations.
2. Exponentiation: **
3. Unary operators: +, -, ~, not
4. Multiplication, division, modulo: *, /, //, %
5. Addition, subtraction: +, -
6. Bitwise shift: <<, >>
7. Bitwise AND: &
8. Bitwise XOR: ^
9. Bitwise OR: |
10. Comparison operators: ==, !=, <, >, <=, >=
11. Logical AND: and
12. Logical OR: or

Importance of Parentheses

While understanding operator precedence is crucial, using parentheses can often improve code readability and prevent unexpected results. By explicitly grouping expressions, you can control the order of evaluation.

Example:

Python

result = (2 + 3) * 4

This expression will result in 20 because the addition is performed first due to the parentheses.

Common Pitfalls

• Incorrect assumptions about precedence: Relying on intuition without checking the actual precedence can lead to errors.
• Overuse of parentheses: Excessive parentheses can make code harder to read. Use them judiciously.