Hello readers! I hope you must be familiar with Python, one of the most popular languages. Python is a high-level and object-oriented programming language. In this article, we will discuss how to copy or clone a list in Python. What is a List? A list is a sequence data type in Python. A list is mutable which means that the values can be modified in the list. A list is used to hold multiple items together. Unlike, C++, a list may contain heterogeneous elements also. By heterogenous, we mean a single list can hold values of different data types. Some of the common list methods are discussed below: : In order to determine the number of items a list may contain, we can use len() function: len() Syntax: len(myList) : myList: A Python list Parameter It returns the length of the string Return Type: This function is used to append an elemet to the end of the list. append(): : Syntax myList.append(myElement) myElement: The element to be added at the end of the list. Parameter: This function is used to clear all the elements from the list. clear(): Syntax: myList.clear() This method when used with a list determines the number of occurrences of a particular element. count(): Syntax: myList.count(myElement) myElement: It represents the element whose number of occurrences is to be determined. Parameters: Return Type: Returns the number of occurrences of myElement in myList. How to copy a list in Python? Python provides us with numerous ways to copy or clone a list in Python. Although these methods are used to accomplish the same task because of different complexities the execution time is different. That is, some methods take lesser time as compared to other methods. These methods are discussed below in detail: This is the easiest and the fastest way to copy a list in Python. This method is quite useful when the programmer wants to modify the list but at the same time wants to maintain an original copy of the list. In this method a copy of the list is made and also a reference to the list is maintained. This procedure of copying a list through the slicing technique is also known as cloning. Using Slice operator: The executing time of this method is around 0.3 seconds. Execution Time: Python provides us with an inbuilt list() method using which we can copy a list easily. This is the simplest method to copy a list as all we need is to call the inbuilt function. This function has the following syntax: Using inbuilt list() method: Syntax: list(iterable) iterable: an object that can be a collection of elements like a set, string, list etc. Parameter: A list containing iterable objects. Return Type: The execution time of this method is around 0.075 seconds. Execution Time: The inbuilt extend() function can be used to copy a list into another. The syntax of this function is given below: Using inbuilt extend() method: Syntax: myList.extend(iterable) iterable: an object that can be a collection of elements like a set, string, list etc. Parameter: Modifies the myList by copying elements from iterable at the end of myList. Return Type: The execution time of this method is around 0.054 seconds. Execution Time: The list comprehension method is used to copy elements individually from one list to another. List comprehension provides us with the simplest and shortest way when we want to make a new list on the basis of an existing list. Using the list comprehension method: The execution time of this method is around 0.217 seconds. Execution Time: In Python, we can use the inbuilt append() function to append elements to the end of a list. This function has the following syntax: Using list append() method: Syntax: myList.append(element) Here, the element is an element that has to be appended at the end of the list. The execution time of this method is around 0.325 seconds. Execution Time: Therefore, we can iterate over the original list using a for-in loop and append each element of the list into another list one by one. Python provides us with the inbuilt copy() method using which we can copy all the elements from one list to another. Using copy() method: The execution time of this method is around 1.488 seconds. Execution Time: In the deep copy method, the process of copying takes place recursively. Firstly, a collection of objects is constructed based on the original list and then the child objects are copied and presented in the original list. In this method, a copy of objects is copied to other objects. Any change made to the copy doesn’t reflect back to the original list. Using deep copy method: In the shallow copy method, a new collection object is constructed and then it is populated with references to the child objects. The recursion is not involved during the copying process therefore, copies of the child objects are not made. In this process, a reference of an object is copied to another object. In contrast to the deep copy method, any change made to the copied object gets reflected back to the original object. Using shallow copy method: We would now demonstrate various methods as discussed above: Example: to demonstrate various methods to copy or clone a list in Python Source Code: Python program Importing library import copy # Statement 1 Function to copy a list using the slice (:) operator def copyListFunction1(myList): # Statement 2 copiedList = myList[:] # Statement 3 return copiedList # Statement 4 Function to copy a list using the inbuilt list() function def copyListFunction2(myList): # Statement 5 copiedList = list(myList) # Statement 6 return copiedList # Statement 7 Function to copy a list using the inbuilt extend() function def copyListFunction3(myList): # Statement 8 copiedList = [] # Statement 9 copiedList.extend(myList) # Statement 10 return copiedList # Statement 11 Function to copy a list using list comprehension technique def copyListFunction4(myList): # Statement 12 copiedList = [element for element in myList] # Statement 13 return copiedList # Statement 14 Function to copy a list using the inbuilt append function def copyListFunction5(myList): # Statement 15 copiedList = [] # Statement 16 for element in myList: # Statement 17 copiedList.append(element) # Statement 18return copiedList # Statement 19 Python program to copy a list using the inbuilt copy() method def copyListFunction6(myList): # Statement 20 copiedList = myList.copy() # Statement 21 return copiedList # Statement 22 Python program to copy a list using the deep copy method def copyListFunction7(myList): # Statement 23 copiedList = copy.deepcopy(myList) # Statement 24 return copiedList # Statement 25 Python program to copy a list using the shallow copy() method def copyListFunction8(myList): # Statement 26 copiedList = copy.copy(myList) # Statement 27 return copiedList # Statement 28 Menu Driver Code originalList = [2, 4, 8, 12, 14, 16] # Statement 29 copiedList1 = copyListFunction1(originalList) # Statement 30 copiedList2 = copyListFunction2(originalList) # Statement 31 copiedList3 = copyListFunction3(originalList) # Statement 32 copiedList4 = copyListFunction4(originalList) # Statement 33 copiedList5 = copyListFunction5(originalList) # Statement 34 copiedList6 = copyListFunction6(originalList) # Statement 35 copiedList7 = copyListFunction7(originalList) # Statement 36 copiedList8 = copyListFunction8(originalList) # Statement 37 print("Original List:", originalList) # Statement 38 print("Copied list 1:", copiedList1) # Statement 39 print("Copied list 2:", copiedList2) # Statement 40 print("Copied list 3:", copiedList3) # Statement 41 print("Copied list 4:", copiedList4) # Statement 42 print("Copied list 5:", copiedList5) # Statement 43 print("Copied list 6:", copiedList6) # Statement 44 print("Copied list 7:", copiedList7) # Statement 45 print("Copied list 8:", copiedList8) # Statement 46 : Output Program Description: In the program; statement 2, statement 5, statement 8, statement 12, statement 15, statement 20, statement 23 and statement 28 corresponds to copyListFunction1, copyListFunction2, copyListFunction3, copyListFunction4, copyListFunction5, copyListFunction6, copyListFunction7 an copyListFunction8 functions respectively. Each of the functions is used to demonstrate the working of methods as discussed above. copyListFunction1: In this function, we have demonstrated how we can clone or copy a list using the slice operator method. This function accepts the original list as a parameter, myList. Inside this function, we have declared a list, copiedList. Using the slice operator, we are copying myList into copiedList. Eventually, the function returns copiedList. : copyListFunction2 In this function, we have demonstrated how we can clone or copy a list using the list() function. This function also accepts the original list as a parameter, myList. Inside this function, we have declared a list, copiedList. We are calling the inbuilt list() function by passing myList as an argument, the result has been stored in copiedList. Eventually, the function returns copiedList. copyListFunction3: In this function, we have demonstrated how we can clone or copy a list using the extend() function. This function also accepts the original list as a parameter, myList. Inside this function, we created an empty list, copiedList. We are invoking the inbuilt extend() function on copiedList by passing myList as an argument. Now, copiedList is the copied or cloned list. Eventually, the function returns copiedList. copyListFunction4: In this function, we have demonstrated how we can clone or copy a list using the extend() function. This function also accepts the original list as a parameter, myList. Inside this function, we created an empty list, copiedList. We are invoking the inbuilt extend() function on copiedList by passing myList as an argument. Now, copiedList is the copied or cloned list. Eventually, the function returns copiedList. copyListFunction5: In this function, we have demonstrated how we can clone or copy a list with the help of the inbuilt append() function. This function also accepts the original list as a parameter, myList. Inside this function, we have created an empty list, copiedList. Now we are iterating over myList using the for-in loop and at each step of the iteration, we are invoking inbuilt append() function on copiedList by passing the current element of the list as an argument. Now, copiedList is the copied or cloned list. Eventually, the function returns copiedList. copyListFunction6: In this function, we have demonstrated how we can clone or copy a list using the inbuilt copy() function. This function also accepts the original list as a parameter, myList. Inside this function, we have declared a list, copiedList. We are invoking the inbuilt copy() function on myList and the result is the copied list that has been stored in the copiedList. Now, copiedList is the copied or cloned list. Eventually, the function returns copiedList. copyListFunction7: In this function, we have demonstrated how we can clone or copy a list using the deep copy method. This function also accepts the original list as a parameter, myList. Inside this function, we have declared a list, copiedList. We are calling the copy.deepcopy() function by passing myList as an argument and the result has been stored in the copiedList. Now, copiedList is the copied or cloned list. Eventually, the function returns copiedList. copyListFunction8: In this function, we have demonstrated how we can clone or copy a list using the shallow copy method. This function also accepts the original list as a parameter, myList. Inside this function, we have declared a list, copiedList. We are calling the copy.copy() function by passing myList as an argument and the result has been stored in the copiedList. Now copiedList is the copied or cloned list. Eventually, the function returns copiedList. In the menu driver code, we have initialized a list of integers, originalList. Then, we have called all the eight functions discussed above by passing originalList as an argument. To store results we have declared eight lists: copiedList1, copiedList2, copiedList3, copiedList4, copiedList5, copiedList6, copiedList7 and copiedList8. Eventually, In statement 38 we are printing the original list to the console and from 39 to 46 we have printed copied lists obtained by using various methods. Firstly, we started with understanding the basics of a list in Python. Then, we learnt about various ways to clone or copy a list in Python. Then, we saw how we can use these methods in practice. We also got a deep understanding of the entire program. Summary: Congratulations! You have moved one more step forward in understanding lists in Python. I hope you enjoyed learning these methods and it will definitely help you to become a good programmer.
