Mutable Madness: Your Python Functions Might Be Lying to You

Clean Python Code: The Case for Immutable Function Arguments

Introduction

In the realm of Python programming, understanding the distinction between mutable and immutable data types is essential for writing clean, predictable code. While mutable objects offer the allure of in-place modification, using them as default arguments in functions can lead to surprising and sometimes problematic side effects. Let’s explore why it’s generally recommended to steer clear of mutable values in Python function arguments.

Mutable vs. Immutable: A Quick Refresher

• Mutable Objects: These are objects whose internal state can be changed after their creation. Common examples include lists, dictionaries, and custom class instances.
• Immutable Objects: These objects cannot be altered after their creation. Integers, strings, and tuples are classic examples.

The Pitfalls of Mutable Default Arguments

Let’s illustrate the issue with a code example:

def add_item(shopping_list=[]):
    shopping_list.append("Coffee")
    return shopping_list

# First call
my_groceries = add_item()…