A Comprehensive Guide on How to Copy Objects in Python

Python is a high-level, interpreted programming language that is widely used in the development of various applications. It provides rich features, including a dynamic type system, memory management, and built-in data structures. One of the core features of Python is its ability to copy objects.

Copying objects in Python is a common task that developers need to perform while working on their applications. There are two types of copy operations that can be performed on objects in Python: shallow copy and deep copy.

In this article, we will explore both shallow and deep copying in Python and discuss how to copy objects using different techniques.

Shallow Copy

Shallow copying creates a new object, which is a copy of the original object, but the new object contains references to the same memory location as the original object. In other words, changes made to the original object will also affect the copy.

In Python, we can perform a shallow copy using the copy method, which is provided by the built-in copy module.

import copy

original_list = [1, 2, 3, [4, 5]]
copy_list = copy.copy(original_list)

print("Original List: ", original_list)
print("Copy List: ", copy_list)

Output:

Original List:  [1, 2, 3, [4, 5]]
Copy List:  [1, 2, 3, [4, 5]]

In the above example, we have created a list original_list containing four elements. We then perform a shallow copy of the list using the copy method and store the result in copy_list. The output shows that both original_list and copy_list contain the same elements.

If we modify an element in, the same change will also be reflected in copy_list.

original_list[3].append(6)

print("Original List: ", original_list)
print("Copy List: ", copy_list)

Output:

Original List:  [1, 2, 3, [4, 5, 6]]
Copy List:  [1, 2, 3, [4, 5, 6]]

As we can see from the output, the change made to original_list also affects copy_list.

Shallow copying can be useful when we want to create a new object that shares some data with the original object. However, if we want to create a completely new object with no references to the original object, we need to perform a deep copy.

Deep Copy

Deep copying creates a new object that is a complete copy of the original object, including all its data and the data of all its nested objects. In other words, changes made to the original object will not affect the copy.

In Python, we can perform a deep copy using the deepcopy method, which is also provided by the copy module.

import copy

original_list = [1, 2, 3, [4, 5]]
deep_copy_list = copy.deepcopy(original_list)

print("Original List: ", original_list)
print("Deep Copy List: ", deep_copy_list)

In the above example, we have created a list original_list containing four elements. We then perform a deep copy of the list using the deepcopy method and store the result in deep_copy_list. The output shows that both original_list.

What's the Difference Between Shallow Copy vs. Deep Copy?

Here is a table summarizing the differences between shallow copy and deep copy in Python: