Coding⏱️ 2 min read📅 2026-06-03

How to Fix: Why updating "shallow" copy dictionary doesn't update "original" dictionary?

Understand how dict.copy() and dict.update() work.

Quick Answer: dict.copy() makes a shallow copy, so changes to the new dictionary don't affect the original. Use dict.clear() or dict.fromkeys() for deep copies.

📋 Table of Contents

  1. 🛠️ Step-by-Step Verified Fixes
  2. 🎯 Final Words

The reason for this behavior lies in the way Python handles mutable default arguments and shallow copies of dictionaries. When you create a new dictionary using `dict.copy()`, it only creates a new reference to the same objects, rather than creating new ones.

🛠️ Step-by-Step Verified Fixes

Method 1: Understanding Shallow Copies

  1. Step 1: Understand that `dict.copy()` creates a shallow copy of the dictionary, which means it only copies the references to the original objects.

Method 2: Using `dict(dict())`

  1. Step 1: Create a new dictionary using `dict(dict())`, which creates a deep copy of the original dictionary.

🎯 Final Words

To avoid this issue, use `dict(dict())` when creating a new dictionary from an existing one. This ensures that you're working with a deep copy of the original dictionary.

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