Python List copy() Method

List Copy() make a new shallow copy of a list.

Example

Python3

# Using list fruits
fruits = ["mango","apple","strawberry"]
# creating a copy shakes
shakes = fruits.copy()
# printing shakes list
print(shakes)

Output

['mango', 'apple', 'strawberry']

Definition and Use of Python List Copy() Method

List Copy() function in Python is used to create a copy of a list. There are two main ways to create a copy of the list Shallow copy and Deep copy. We will discuss the list copy() methods in detail below.

Python List copy() function is used to create a copy of a list, which can be used to work and it will not affect the values in the original list. This gives freedom to manipulate data without worrying about data loss.

List copy() Method Syntax

list.copy()

Parameters

• The copy() method doesn’t take any parameters.

Returns: Returns a shallow copy of a list. A shallow copy means any modification in the new list won’t be reflected in the original list. 

How to Create a Simple Copy list in Python

Copying and creating a new list in Python can be done using copy() function in Python.

Python3

# Using List girls
girls = ["Priya","Neha","Radha","Nami"]
# Creating new copy
girlstudent = girls.copy()
#printing new list
print(girlstudent)

Output

['Priya', 'Neha', 'Radha', 'Nami']

More Examples on List copy() Method

Let us see a few examples of the list copy() method in Python.

Example 1: Simple List Copy

In this example, we are creating a List of Python strings and we are using copy() method to copy the list to another variable.

Python3

lis = ['Geeks','for','Geeks']
new_list = lis.copy()
print('Copied List:', new_list)

Output

Copied List: ['Geeks', 'for', 'Geeks']

Example 2: Demonstrating the working of List copy() 

Here we will create a Python list and then create a shallow copy using the copy() function in Python. Then we will append a value to the copied list to check if copying a list using copy() method affects the original list.

Python3

# Initializing list
lis1 = [ 1, 2, 3, 4 ]

# Using copy() to create a shallow copy
lis2 = lis1.copy()

# Printing new list
print ("The new list created is : " + str(lis2))

# Adding new element to new list
lis2.append(5)

# Printing lists after adding new element
# No change in old list
print ("The new list after adding new element : \
" + str(lis2))
print ("The old list after adding new element to new list  : \
" + str(lis1))

Output

The new list created is : [1, 2, 3, 4]
The new list after adding new element : [1, 2, 3, 4, 5]
The old list after adding new element to new list  : [1, 2, 3, 4]

Note: A shallow copy means if we modify any of the nested list elements, changes are reflected in both lists as they point to the same reference.

Shallow Copy and Deep Copy

A deep copy is a copy of a list, where we add an element in any of the lists, only that list is modified. 

In list copy() method, changes made to the copied list are not reflected in the original list. The changes made to one list are not reflected on other lists except for in nested elements (like a list within a list).

We can use the copy.deepcopy() from the copy module to avoid this problem.

• Techniques to deep copy: 
  • Using copy.deepcopy()
• Techniques to shallow copy:
  • Using copy.copy()
  • Using list.copy()
  • Using slicing

To gain a deeper understanding, Refer to this article on Deep Copy vs Shallow Copy. 

Example 3: Demonstrating Techniques of Shallow and Deep copy  

Here we will create a list and then create a shallow copy using the assignment operator, list copy() method, and copy.copy() method of the Python copy module.

We also create a deep copy using deepcopy() in Python. Then we will make changes to the original list and see if the other lists are affected or not.

Python3

import copy

# Initializing list
list1 = [ 1, [2, 3] , 4 ]
print("list 1 before modification:\n", list1)

# all changes are reflected
list2 = list1

# shallow copy - changes to
# nested list is reflected,
# same as copy.copy(), slicing

list3 = list1.copy()

# deep copy - no change is reflected
list4 = copy.deepcopy(list1)

list1.append(5)
list1[1][1] = 999

print("list 1 after modification:\n", list1)
print("list 2 after modification:\n", list2)
print("list 3 after modification:\n", list3)
print("list 4 after modification:\n", list4)

Output

list 1 before modification:
 [1, [2, 3], 4]
list 1 after modification:
 [1, [2, 999], 4, 5]
list 2 after modification:
 [1, [2, 999], 4, 5]
list 3 after modification:
 [1, [2, 999], 4]
list 4 after mo...

Copy List Using Slicing

Here we are copying the list using the list slicing method [:] and we are appending the ‘a’ to the new_list. After printing we can see the newly appended character ‘a’ is not appended to the old list.

Python3

list = [2,4,6]
new_list = list[:]
new_list.append('a')
print('Old List:', list)
print('New List:', new_list)

Output

Old List: [2, 4, 6]
New List: [2, 4, 6, 'a']

We discussed the definition, syntax and examples of Python copy() method. Python copy() function is very useful when working with sensitive data and you can’t risk mistakes.

We also briefly talked about shallow vs deep copy. Hope this helped you in understanding copy() function in Python.