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Python | Cloning or Copying a list

  • Difficulty Level : Basic
  • Last Updated : 06 Jan, 2022

In this article we will go through various ways of copying or cloning a list in Python. These various ways of copying takes different execution time, so we can compare them on the basis of time. 

1. Using slicing technique 
This is the easiest and the fastest way to clone a list. This method is considered when we want to modify a list and also keep a copy of the original. In this we make a copy of the list itself, along with the reference. This process is also called cloning. This technique takes about 0.039 seconds and is the fastest technique. 

Python3




# Python program to copy or clone a list
# Using the Slice Operator
def Cloning(li1):
    li_copy = li1[:]
    return li_copy
   
# Driver Code
li1 = [4, 8, 2, 10, 15, 18]
li2 = Cloning(li1)
print("Original List:", li1)
print("After Cloning:", li2)

Output: 

Original List: [4, 8, 2, 10, 15, 18] 
After Cloning: [4, 8, 2, 10, 15, 18] 

2. Using the extend() method 
The lists can be copied into a new list by using the extend() function. This appends each element of the iterable object (e.g., another list) to the end of the new list. This takes around 0.053 second to complete. 

Example: 

Python3




# Python code to clone or copy a list
# Using the in-built function extend()
def Cloning(li1):
    li_copy = []
    li_copy.extend(li1)
    return li_copy
   
# Driver Code
li1 = [4, 8, 2, 10, 15, 18]
li2 = Cloning(li1)
print("Original List:", li1)
print("After Cloning:", li2)

Output: 

Original List: [4, 8, 2, 10, 15, 18]
After Cloning: [4, 8, 2, 10, 15, 18]

3. Using the list() method 
This is the simplest method of cloning a list by using the built-in function list(). This takes about 0.075 seconds to complete. 

Example: 

Python3




# Python code to clone or copy a list
# Using the in-built function list()
def Cloning(li1):
    li_copy = list(li1)
    return li_copy
   
# Driver Code
li1 = [4, 8, 2, 10, 15, 18]
li2 = Cloning(li1)
print("Original List:", li1)
print("After Cloning:", li2)

Output: 

Original List: [4, 8, 2, 10, 15, 18]
After Cloning: [4, 8, 2, 10, 15, 18]

4. Using the method of Shallow Copy 
This method of copying using copy.copy is well explained in the article Shallow Copy. This takes around 0.186 seconds to complete. 

5. Using list comprehension 
The method of list comprehension can be used to copy all the elements individually from one list to another. This takes around 0.217 seconds to complete. 

Python3




# Python code to clone or copy a list
# Using list comprehension
def Cloning(li1):
    li_copy = [i for i in li1]
    return li_copy
   
# Driver Code
li1 = [4, 8, 2, 10, 15, 18]
li2 = Cloning(li1)
print("Original List:", li1)
print("After Cloning:", li2)

Output: 

Original List: [4, 8, 2, 10, 15, 18]
After Cloning: [4, 8, 2, 10, 15, 18]

6. Using the append() method 
This can be used for appending and adding elements to list or copying them to a new list. It is used to add elements to the last position of list. This takes around 0.325 seconds to complete and is the slowest method of cloning. 

Python3




# Python code to clone or copy a list
# Using append()
def Cloning(li1):
    li_copy =[]
    for item in li1: li_copy.append(item)
    return li_copy
   
# Driver Code
li1 = [4, 8, 2, 10, 15, 18]
li2 = Cloning(li1)
print("Original List:", li1)
print("After Cloning:", li2)

Output: 

Original List: [4, 8, 2, 10, 15, 18]
After Cloning: [4, 8, 2, 10, 15, 18]

7. Using the copy() method 
The inbuilt method copy is used to copy all the elements from one list to another. This takes around 1.488 seconds to complete.

 Example: 

Python3




# Python code to clone or copy a list
# Using bilt-in method copy()
def Cloning(li1):
    li_copy =[]
    li_copy = li1.copy()
    return li_copy
   
# Driver Code
li1 = [4, 8, 2, 10, 15, 18]
li2 = Cloning(li1)
print("Original List:", li1)
print("After Cloning:", li2)

Output: 

Original List: [4, 8, 2, 10, 15, 18]
After Cloning: [4, 8, 2, 10, 15, 18]

8. Using the method of Deep Copy 
This method of copying is well explained in the article Deep Copy. This takes around 10.59 seconds to complete and is the slowest method of cloning. 

Referred to Stack Overflow.
 


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