How to Use Copy Module in Python: Syntax and Examples

Use the copy module in Python to create shallow or deep copies of objects. Import it with import copy, then use copy.copy() for a shallow copy and copy.deepcopy() for a deep copy.

Syntax

The copy module provides two main functions:

• copy.copy(obj): Creates a shallow copy of obj. It copies the object but not nested objects inside it.
• copy.deepcopy(obj): Creates a deep copy of obj. It copies the object and all nested objects recursively.

First, import the module with import copy.

python

import copy

shallow_copy = copy.copy(original_object)
deep_copy = copy.deepcopy(original_object)

Example

This example shows the difference between shallow and deep copy using a list that contains another list inside it.

python

import copy

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

# Change nested list in shallow copy
shallow[2][0] = 'changed'

print('Original:', original)
print('Shallow copy:', shallow)
print('Deep copy:', deep)

Output

Original: [1, 2, ['changed', 4]]
Shallow copy: [1, 2, ['changed', 4]]
Deep copy: [1, 2, [3, 4]]

Common Pitfalls

A common mistake is to use copy.copy() when you need a full independent copy of nested objects. Shallow copy only copies the outer object, so changes to nested objects affect both copies.

Always use copy.deepcopy() if you want to avoid shared nested objects.

python

import copy

original = [[1, 2], 3]
shallow = copy.copy(original)
shallow[0][0] = 'oops'

print('Original after shallow copy change:', original)

# Correct way
original = [[1, 2], 3]
deep = copy.deepcopy(original)
deep[0][0] = 'safe'
print('Original after deep copy change:', original)

Output

Original after shallow copy change: [['oops', 2], 3]
Original after deep copy change: [[1, 2], 3]

Quick Reference

Function	Description
copy.copy(obj)	Shallow copy: copies object but shares nested objects
copy.deepcopy(obj)	Deep copy: copies object and all nested objects
import copy	Import the copy module to use its functions

Key Takeaways

Import the copy module with import copy to use copying functions.

Use copy.copy() for a shallow copy that shares nested objects.

Use copy.deepcopy() for a full independent copy including nested objects.

Shallow copies can cause bugs if nested objects are modified.

Deep copy is safer for complex objects but slower.