A list is a collection of comma-separated values within square brackets. Python lists allow us to work with multiple types of elements at once. List are mutable i.e. values in the list can be modified which means new list will not created when you make changes to an element of a list

For Example :

# a list of different languages
['French', 'English', 'Hindi']

Creating Lists

In Python, a list is created by placing elements inside square brackets [], separated by commas.

# list of integers
l = [1, 2, 3]
                

A list can have any number of items and they can be of different types (integer, float, string, etc.).

# empty list
l = []

# list with different data types
l1 = [1, "Hello", 3.4]
    

A list can also have another list inside it. This is called a nested list.

# nested list
l = ["Hello", [8, 4, 6], ['a','b','c']]

Accessing List Elements

There are various ways in which we can access the elements of a list.

Indexing :

In Python, indexing starts from 0. We can access an item in a list through []. So, a list having 5 elements will have an index from 0 to 4.

The index must be an integer. We can't use float or other types, this will result in "TypeError". Nested lists are accessed using nested indexing.

Let us see the Example below :

Output :

Negative Indexing :

Python also allows negative indexing for lists . The index of -1 refers to the last item, -2 to the second last item and so on.

Let us see the Example below :

Output :

Slicing :

In Python we can access a section of items from the list through slicing using [:] operator. It is an operation in which we slice a particular range of items from that list. A slice of a list is basically its sub-list.

Let us see the Example below :

Output :

Here,

• mylist[2:5] returns a list with items from index 2 to index 4.


• mylist[5:] returns a list with items from index 5 to the end.


• mylist[:] returns all list items

Note : When we slice lists, the start index is included but the end index is excluded (i.e. including start index to (end index-1)).

Membership Testing :

Membership Testing is an operation to check if an item exists in the list or not using 'in' keyword. For example,

Let us see the Example below :

Here,

• 'Hindi' is not present in lang, 'Hindi' in lang evaluates to False.


• 40 is present in lang, 40 in lang evaluates to True.

len() Function

In Python, we use the len() method to find the number of elements present in a list.

For Example,

Python List Methods

Python has many useful list methods that makes it really easy to work with lists.

Method	Description
append()	add an item to the end of the list
insert()	inserts an item at the specified index
extend()	add items of lists and other iterables to the end of the list
index()	returns the index of the first matched item
remove()	removes item present at the given index
sort()	sort the list in ascending/descending order
count()	returns the count of the specified item in the list
pop()	returns and removes item present at the given index
reverse()	reverses the items of the list
del statement	remove the specified element from the list

Built-in Methods of Python Lists

append()

The append() method adds an item at the end of the list.

For example,

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insert()

This function is used to insert an element at a specified index. This function takes 2 argument the index where an item to be inserted and the item itself

For example,

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extend()

We use the extend() method to add all items of one list to another.

For example,

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index()

It returns the index of first matched item from the list. It returns the first occurrence of an item for which the index position is to be searched in the list.

For example,

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remove()

It removes the first occurrence of item from the list. A ValueError exception is raised if item is not found in the list.

For example,

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sort()

Sort the elements of the list in ascending order (i.e. from the lowest value to the highest value). By default it sorts the element in ascending order, if we want to sort the list in descending order we need to write

>>> list_name.sort(reverse=True)

For example,

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reverse()

It reverses the order of the elements in a list. This function reverses the item of the list. It replaces a new value "in place" of item that already exists in the list i.e. it does not create a new list.

For example,

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count()

It counts how many times an element has occurred in a list and returns it.

For example,

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pop()

It remove the element from the specified index and also returns the element which was removed

For example,

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del Statement