How to clone or copy a list in Python?

The list in Python is a sequence data type that is used to store various types of data. A list is created by placing each data element inside square brackets "[]" and these are separated by commas.

In Python, the assignment operator doesn't create a new object; rather, it gives another name to an already existing object. This can be verified by id() function

>>> L1 = [1,2,3,4]
>>> L2 = L1
>>> id(L1)
185117137928
>>> id(L2)
185117137928 

There are various ways of cloning/copying a list in Python. In this article, we will discuss some of them.

Cloning a List Using Assignment Operator

The simplest way of cloning a list is by assigning an old list object to the new object. Here we need to use the assignment operator "=".

Syntax

Following is the syntax to copy the list using the assignment operator in Python -

Old_list = new_list

Example

The assignment operator doesn't create a new list object; rather, it gives another name to an already existing object. As we can see in the above example, the IDs of both objects are the same, which is verified by the id() function.

If we make changes in any of the lists, the other one also gets changed, so if we want to keep the original list unchanged, the following methods can be used.

l1 = [1,2,3,4]
l2 = l1
print("Original List:", l1)
print("After Cloning:", l2)

print("ID of Original list", id(l1))
print("ID of copied list", id(l2))

Following is an output of the above code -

Original List: [1, 2, 3, 4]
After Cloning: [1, 2, 3, 4]
ID of Original list 140565795507408
ID of copied list 140565795507408

Cloning a List using List slicing

The slicing technique in Python is used to access a range of items in a list. This technique can also be used for cloning a list, where we want to modify a list and also keep a copy of the original.

Syntax

Following is the syntax to copy the list using list slicing in Python -

list_obj[start:stop:step]

Example

From the above example, it has been proven that the slicing technique of a list can also be used for cloning a list.

l1 = [1,2,3,4]
l2= l1
print("Original List:", l1)
print("After Cloning:", l2)

print("ID of Original list", id(l1))
print("ID of copied list", id(l2))

l2.append(10)
print('Original list',l1)
print('Copied and updated list',l2)

Following is an output of the above code -

Original List: [1, 2, 3, 4]
After Cloning: [1, 2, 3, 4]

ID of Original list 140565661890112
ID of copied list 140565795507408

Original list [1, 2, 3, 4]
Copied and updated list [1, 2, 3, 4, 10]

Cloning a List using copy() Method

The copy() is a Python list method that is used to get a shallow copy of the list. It means if we do any modification of the new list, those changes will not be reflected in the original list.

Syntax

Following is the syntax to copy a list using the copy() method in Python -

new_list = list.copy()

Example

The list.copy() method also successfully cloned a list. The cloned list object "l2" is created with the id 140565662101664.

l1 = [1,2,3,4]
l2 = l1.copy()
print("Original List:", l1)
print("After Cloning:", l2)

print("ID of Original list", id(l1))
print("ID of copied list", id(l2))

l2.append(10)
print('Original list',l1)
print('Copied and updated list',l2)

Following is an output of the above code -

Original List: [1, 2, 3, 4]
After Cloning: [1, 2, 3, 4]
ID of Original list 140565661966976
ID of copied list 140565662101664
Original list [1, 2, 3, 4]
Copied and updated list [1, 2, 3, 4, 10]

Cloning a List using the list() Method

The list() method is also considered the simplest way of cloning a list. This function creates a new list object. Let's take an example and see how the list() method clones a Python list.

Example

Here, we have copied the list, l1 to the list l2 using list() function -

l1 = [1,2,3,4]
# clone a list
l2 = list(l1)
print("Original List:", l1)
print("After Cloning:", l2)

print("ID of Original list", id(l1))
print("ID of copied list", id(l2))

l2.append(10)
print('Original list',l1)
print('Copied and updated list',l2)

Following is an output of the above code -

Original List: [1, 2, 3, 4]
After Cloning: [1, 2, 3, 4]
ID of Original list 140565661915808
ID of copied list 140565661713424
Original list [1, 2, 3, 4]
Copied and updated list [1, 2, 3, 4, 10]	

All these are some of the different ways to clone a Python list. Also, we can use list comprehension, extend(), and append() methods to clone a list.