Are You Really Copying in Python? 🤯 Shallow vs Deep Copy Explained

#python #programming #algorithms #development

Understanding the difference between shallow copy and deep copy is key when working with mutable objects in Python like lists, dictionaries, or custom classes.

📦 What is a Shallow Copy?

A shallow copy creates a new object, but inserts references to the original objects inside it.

✅ Example:

import copy

original = [[1, 2], [3, 4]]
shallow = copy.copy(original)

shallow[0][0] = 99

print(original)  # [[99, 2], [3, 4]]

🎯 Original is affected because inner objects are shared.

🌊 What is a Deep Copy?

A deep copy creates a new object and recursively copies all nested objects.

✅ Example:

import copy

original = [[1, 2], [3, 4]]
deep = copy.deepcopy(original)

deep[0][0] = 99

print(original)  # [[1, 2], [3, 4]]

✅ Original is NOT affected because everything is duplicated.

🔍 Comparison Table

Feature	Shallow Copy	Deep Copy
New outer object?	✅ Yes	✅ Yes
New inner objects?	❌ No (shared)	✅ Yes (copied)
Uses `copy.copy()`	✅	❌
Uses `copy.deepcopy()`	❌	✅

🧪 When to Use Which?

Use shallow copy if:
- Your object has only immutable or flat structure
- You want faster performance
Use deep copy if:
- Your object has nested mutable objects
- You want full isolation