Python update list by index

How to create add update delete List Python

In this article, we will learn how to create add update delete List Python for beginners. Also, we will learn how to create a Python list and different types of lists, how to access list elements, How to add elements to the List, How to delete elements from the list, How to update the list, and How to Slicing of lIst.

What is Python List

The list is a sequential and ordered collection data type in Python that is represented by square brackets([]) and each item in the list is separated by a comma(,). The List can store elements of any data type like (string, boolean, int) that are changeable(item can be removed, added, updated once created), or duplicated. It is similar to a dynamic array in other languages (ArrayList in C#, Java). We can store data of different types of objects in a single list.

1. How to Create a List empty list in Python

• Lists in python are created by placing the elements in square brackets[] separated by a comma.
• Using the List constructor list() , which is used to create a list.

1.1 Create single list in Python using [] brackets

In this below example we have created an empty list using [] bracket, a list of strings, and a list of mixed datatypes As we can see a list can have different types of elements(int, float, string) as well as duplicate items.

print('Different ways to create a List :') #an empty list alph_List = [] print(alph_List) #list of string pre_List = ['at','on','into','up','up'] print(pre_List) #list of mixed data types mixed_type_list = [12,24,2.5,2.5,'upto'] print(mixed_type_list ) #list of number num_list = [10,20,30,40,10] print(num_list)

#nested list of mixed data-types pre_List = [['at','on','into'],[12,24,2.5,2.5]] print('Nested List:') print(pre_List)

Nested List: [['at', 'on', 'into'], [12, 24, 2.5, 2.5]]

1.3. Create a list using a List constructor

To create a list using the list constructor we pass the elements in the list() constructor.

Syntax

#create list using list constructor listname = list((element1-----elementn))

#create a list using list constructor pre_list = list(("at", "up",20,30,2.5,4.5)) print(pre_list) #create nested list using list constructor nested_list = list((["at", "up",20,30,2.5,4.5],[12,34,16])) print(nested_list )

['at', 'up', 20, 30, 2.5, 4.5] [['at', 'up', 20, 30, 2.5, 4.5], [12, 34, 16]]

2. How to Access List elements in Python

There are three ways to access elements of the list.

2.1 Access Python List element using Positive Index

List element is accessed by an index by providing the index of the element in square brackets([]). The index of the list elements starts from 0 and so on. A list of n elements will have an index range of start index is 0 and the last index is n-1.

Syntax

Important Note:

• The index must be an integer type, it can not be a float.
• To avoid IndexError (out of range) pass index in range, A list has 7 elements, has index range will be 0 to 6, accessing index except these indexes will throw IndexError: out of range exception.

Python Program to Access list element by positive index

pre_List = ['at','on','into','up','The'] print('Accessing single list:') print(pre_List[1]) print(pre_List[3]) print(pre_List[4]) print('\n Accessing nested list:') nested_list = list((["at", "up",20,30,2.5,4.5],[12,34,16])) print(nested_list[0][1]) print(nested_list[0][2]) print(nested_list[0][3]) print(nested_list[1][1]) #passing an index of float type print(pre_List[1.3])

Accessing elements of a single list by Index: on up The Accessing elements of a nested list by Index: up 20 30 34 Traceback (most recent call last): File "main.py", line 27, in print(pre_List[1.3]) TypeError: list indices must be integers or slices, not float

2.2 Access python List elements Using Negative Indexing

The list element is accessed by providing the Negative index in the square bracket([]) the negative index starts from the end. So -1 is for the first last element, -2 for the second last element, and so on till the list length.

Python Program to Access list elements by Negative Index

#Accessing single list element by negative Index pre_List = ['at','on','into','up','The'] print('Accessing single list element by negative Index:') print(pre_List[-1]) print(pre_List[-2]) print(pre_List[-3]) print(pre_List[-4]) print(pre_List[-5]) #Accessing nested list by negative Index print('\nAccessing nested list by negative Index:') nested_list = list(([ "up",30,2.5,4.5],[12,34,"at"])) print(nested_list[0][-1]) print(nested_list[0][-2]) print(nested_list[0][-3]) print(nested_list[0][-4]) print(nested_list[1][-1]) print(nested_list[1][-2]) print(nested_list[1][-3])

Accessing single list element by negative Index: The up into on at Accessing nested list by negative Index: 4.5 2.5 30 up at 34 12

2.3 Access Python List element Using Range of Indexes

We access the range of elements by index we pass the start and end index in a square bracket([]). It returns a new list of elements those fall in the index range.

Python Program to Access mutiple elements by Range of Indexes

pre_List = ['at','on','into','up','The'] print('Accessing list element range of indexes:\n') print(pre_List[1:4]) print(pre_List[0:3]) print(pre_List[0:5])

Accessing list element range of indexes: ['on', 'into', 'up'] ['at', 'on', 'into'] ['at', 'on', 'into', 'up', 'The']

Accessing list elements by Range of negative Indexes

pre_List = ['at','on','into','up','The'] print('Accessing list element range of negative indexes:\n') print(pre_List[-4:-1]) print(pre_List[-3:-2]) print(pre_List[-3:-1])

Accessing list element range of negative indexes: ['on', 'into', 'up'] ['into'] ['into', 'up']

3. How to slice a list in Python

: slicing operator is used to do slicing in Python. It returns the new list of elements that pass the given slicing range from the existing list.

Python Program to slice list elements

pre_List = ['at','on','into','up','The'] #start from index 1 to end at 3, element at index 3 (will not be included) print(pre_List[1:3]) #start from index 0 to end at 3, element at index 3 (will not be included) print(pre_List[:3]) #element at index 3 till end of list print(pre_List[3:]) #print the whole list start to end print(pre_List[:]) # from 2 last element to start(index 0) print(pre_List[:-2])

['on', 'into'] ['at', 'on', 'into'] ['up', 'The'] ['at', 'on', 'into', 'up', 'The'] ['at', 'on', 'into']

4. How to get Length of a List in Python

The Len() method is used to get the length of the list in Python

pre_List = ['at','on','into','up','The'] #len() method to get length of list List_len = len(pre_List) print('list Length :',List_len)

Output

5. How to add elements in Python List

4.1 Add/append an element to Python List using Append()

The append() method of the list is to append an element, iterable( list, tuple, string, dictionary, set) append in the list. The size of the list change after appending the element to the list.

Note: The iterable will append as an object at end of the list not one by one element of iterable.

Python Program to add elements to Python List

orginal_list = ['at','on','into'] num_list = [12,13] my_dict = my_set = my_str = 'upon' print('before append element:\n',orginal_list) #appending an element orginal_list.append('data') #appending an list orginal_list.append(num_list) #appending a dict orginal_list.append(my_dict) #appending a set orginal_list.append(my_set) #appending a string orginal_list.append(my_str) print('original list with appended element:\n',orginal_list)

before append element: ['at', 'on', 'into'] original list with an appended element: ['at', 'on', 'into', 'data', [12, 13], , , 'upon']

4.2 Add mutiple elements to Python list using Extend()

Extend() method adds iterable(list, tuple, string, dictionary, set) at the end of the list, unlike append it iterates over elements of iterable and adds one by one to the end of the list.

Note: the size of the list increase by the number of elements in each iterable.

#extend() iterable to list orginal_list = ['at','on'] num_list = [12,13] my_dict = my_set = my_str = 'upon' print('before extend iterable:\n',orginal_list) #appending an element orginal_list.extend('data') #extending an list orginal_list.extend(num_list) #extending a dict orginal_list.extend(my_dict) #extending a set orginal_list.extend(my_set) #extending a string orginal_list.extend(my_str) print('original list after extended iterables:\n',orginal_list) print('list length :',len(orginal_list))

list before extend iterable: ['at', 'on'] original list after extended iterables: ['at', 'on', 'd', 'a', 't', 'a', 12, 13, 'A', 'B', 1, 2, 'u', 'p', 'o', 'n'] list length : 16

4.3Add element at a specific index in Python List

Insert() method add multiple elements at a specific index in the list. The first argument is an index and the second is an element we want to insert.

original_list = ['at','on','up'] #inserting at index 0 original_list.insert(0,14) #inserting at index 1 original_list.insert(1,12) #inserting at index 2 original_list.insert(2,'onto') print(original_list)

5. How to update a list in Python

A list in Python is updated using the = operator or slicing. Let us understand with an example how to achieve this.

Python Program to update a list in Python

original_list = ['at','on','up'] #updating list elemnst at 0 index original_list[0] = 'above' #update element using slicing original_list[3:5] = ['in','into'] print(original_list)

6. How to delete elements from a List in Python

These are methods to delete or remove elements from the list.

• Del: The delstatement is used to delete item by index,single, multiple elements, or a whole list.
• Pop() : It removes elements at specific Index.
• remove() : It is used to remove the passed element as a parameter.
• clear() : It clear() the list.

Python Program to Delete elements from List using Del

original_list = ['at','on','up','in','upon'] # delete single element del original_list[1] print('after deletion:',original_list) # delete multiple items del original_list[1:4] print('after deletion :',original_list) # delete the full list del original_list

after deletion: ['at', 'up', 'in', 'upon'] after deletion: ['at']

Python Program to Delete elements Using Pop(),remove(),clear()

original_list = ['at','on','up','in','upon'] # delete a single element at index 1 original_list.pop(1) print('after pop() :',original_list) # removing the 'upon' from the list original_list.remove('upon') print('after remove() :',original_list) # clear the full list original_list.clear() print('after clear() :',original_list)

after pop() : ['at', 'up', 'in', 'upon'] after remove() : ['at', 'up', 'in'] after clear() : []

Conclusion:

In this post we understood How to create add update delete List Python that also includes what is a list, and how to create, add, delete, and update elements from a List with code examples.

Источник