Python Dictionary Copy Vs Deep Copy

In Python, Dictionary like other non-primitive data structures can be copied using various methods. The key distinction lies in the depth of the copy. In this article, we are going to learn about deep copy and shallow copy in Python.

What is Shallow Copy in Python Dictionary?

In Python, a shallow copy creates a new object that references the same underlying data of the original object. This means although the objects have different names, both objects point to the same memory location. So if you make changes in either of the objects then the changes will affect both objects.

• Creates a new dictionary with the same structure (key-value pairs) as the original, but the values themselves are references to the original objects.
• Any changes made to mutable objects within the copied dictionary will also affect the original dictionary

Example

The code you’ve provided does indeed demonstrate Shallow copy in Python dictionaries.

Python

import copy

# Original dictionary
original_dict = {'a': 1, 'b': [1, 2, 3]}
print("Original Dictionary:", original_dict)

# Shallow copy
shallow_copy = copy.copy(original_dict)
print("Shallow Copy:", shallow_copy)

# Modifying data in shallow copy
shallow_copy['b'][1] = 4

# Printing the dictionary after change
print("Original Dictionary After Change:", original_dict)

# Printing the Copy After Change
print("Shallow Copy After Change:", shallow_copy)

Output

{'a': 1, 'b': [1, 2, 3]}
{'a': 1, 'b': [1, 2, 3]}
{'a': 1, 'b': [1, 4, 3]}
{'a': 1, 'b': [1, 4, 3]}

Or You can Also make a shallow Copy of Dictionary by copy method by importing copy module

shallow_copy = original_dict.copy()

What is Deep Copy in Python Dictionary

In Python, a Deep copy creates a completely new object. The objects have different names but here both object will not point to the same memory location. So if you make changes in either of the objects then the changes will not affect both the objects.

• Creates a completely independent copy of both the dictionary’s structure and all of its values, including nested mutable objects.
• Changes made to the copied dictionary won’t affect the original.

Example

The code you’ve provided does indeed demonstrate deep copy in Python dictionaries.

Python

import copy

# Original dictionary
original_dict = {"a": 1, "b": [1, 2, 3]}
print("Original Dictionary:", original_dict)

# Perform a deep copy
deep_copy = copy.deepcopy(original_dict)
print("Deep Copy:", deep_copy)

# Modify the deep copy
deep_copy["b"][1] = 4

# Print both dictionaries to see the changes
print("Original Dictionary after modifying deep copy:", original_dict)
print("Deep Copy after modification:", deep_copy)

Output

{'a': 1, 'b': [1, 2, 3]}
{'a': 1, 'b': [1, 2, 3]}
{'a': 1, 'b': [1, 2, 3]}
{'a': 1, 'b': [1, 4, 3]}

Difference Between Deep Copy and Shallow Copy

Feature	Shallow Copy	Deep Copy
Definition	Shallow copy creates a new object, but it references the same objects in the original structure.	Deep copy creates a new object and recursively copies all objects found in the original.
Memory Usage	Consumes less memory as it shares reference to the objects.	Consumes high memory as compared to shallow copy.
Copied Objects	Changes made in nested object will reflect in both original and copied structure.	Changes made in nested object will not reflect in both original and copied structure.
Performance	Faster to create as it does not involve in copying nested object.	Slower to create due to recursive copying of all objects
Dependency	Dependent on structure. changes in nested objects affect both the original and the copy.	Independent on structure. changes in nested objects only affect the copy, not the original.