Python List

In Python, lists allow us to store multiple items in a single variable. For example, if you need to store the ages of all the students in a class, you can do this task using a list.

Lists are similar to arrays (dynamic arrays that allow us to store items of different data types) in other programming languages.

Create a Python List

We create a list by placing elements inside square brackets [], separated by commas. For example,

# a list of three elements
ages = [19, 26, 29]
print(ages)

Output

[19, 26, 29]

Here, the ages list has three items.

List Items of Different Types

Python lists are very flexible. We can also store data of different data types in a list. For example,

# a list containing strings, numbers and another list
student = ['Jack', 32, 'Computer Science', [2, 4]]
print(student)

# an empty list
empty_list = []
print(empty_list)

List Characteristics

In Python, lists are:

• Ordered - They maintain the order of elements.
• Mutable - Items can be changed after creation.
• Allow duplicates - They can contain duplicate values.

Access List Elements

Each element in a list is associated with a number, known as an index. The index of first item is 0, the index of second item is 1, and so on.

We use these indices to access items of a list. For example,

languages = ['Python', 'Swift', 'C++']

# access the first element
print('languages[0] =', languages[0])

# access the third element
print('languages[2] =', languages[2])

Output

languages[0] = Python
languages[2] = C++

Negative Indexing

In Python, a list can also have negative indices. The index of the last element is -1, the second last element is -2 and so on.

Let's see an example.

languages = ['Python', 'Swift', 'C++']

# access the last item
print('languages[-1] =', languages[-1])

# access the third last item
print('languages[-3] =', languages[-3]) 

Output

languages[-1] = C++
languages[-3] = Python

Slicing of a List in Python

If we need to access a portion of a list, we can use the slicing operator, :. For example,

my_list = ['p', 'r', 'o', 'g', 'r', 'a', 'm']
print("my_list =", my_list)

# get a list with items from index 2 to index 4 (index 5 is not included)
print("my_list[2: 5] =", my_list[2: 5])    

# get a list with items from index 2 to index -3 (index -2 is not included)
print("my_list[2: -2] =", my_list[2: -2])  

# get a list with items from index 0 to index 2 (index 3 is not included)
print("my_list[0: 3] =", my_list[0: 3])

Output

my_list = ['p', 'r', 'o', 'g', 'r', 'a', 'm']
my_list[2: 5] = ['o', 'g', 'r']
my_list[2: -2] = ['o', 'g', 'r']
my_list[0: 3] = ['p', 'r', 'o']

Omitting Start and End Indices in Slicing

If you omit the start index, the slicing starts from the first element. Similarly, if you omit the last index, the slicing ends at the last element. For example,

my_list = ['p', 'r', 'o', 'g', 'r', 'a', 'm']
print("my_list =", my_list)

# get a list with items from index 5 to last
print("my_list[5: ] =", my_list[5: ])

# get a list from the first item to index -5
print("my_list[: -4] =", my_list[: -4])

# omitting both start and end index
# get a list from start to end items
print("my_list[:] =", my_list[:])

Output

my_list = ['p', 'r', 'o', 'g', 'r', 'a', 'm']
my_list[5: ] = ['a', 'm']
my_list[: -4] = ['p', 'r', 'o']
my_list[:] = ['p', 'r', 'o', 'g', 'r', 'a', 'm']

To learn more about slicing, visit Python program to slice lists.

Note: If the specified index does not exist in a list, Python throws the IndexError exception.

Add Elements to a Python List

As mentioned earlier, lists are mutable and we can change items of a list. To add an item to the end of a list, we can use the list append() method. For example,

fruits = ['apple', 'banana', 'orange']
print('Original List:', fruits)

fruits.append('cherry')

print('Updated List:', fruits)

Output

Original List: ['apple', 'banana', 'orange']
Updated List: ['apple', 'banana', 'orange', 'cherry']

Add Elements at the Specified Index

We can insert an element at the specified index to a list using the insert() method. For example,

fruits = ['apple', 'banana', 'orange']
print("Original List:", fruits) 

fruits.insert(2, 'cherry')

print("Updated List:", fruits)

Output

Original List: ['apple', 'banana', 'orange']
Updated List: ['apple', 'banana', 'cherry', 'orange']

Add Elements to a List From Other Iterables

The list extend() method method all the items of the specified iterable, such as list, tuple, dictionary or string , to the end of a list. For example,

numbers = [1, 3, 5]
print('Numbers:', numbers)

even_numbers  = [2, 4, 6]
print('Even numbers:', numbers)

# adding elements of one list to another
numbers.extend(even_numbers)

print('Updated Numbers:', numbers) 

Output

Numbers: [1, 3, 5]
Even numbers: [2, 4, 6]
Updated Numbers: [1, 3, 5, 2, 4, 6]

Change List Items

We can change the items of a list by assigning new values using the = operator. For example,

colors = ['Red', 'Black', 'Green']
print('Original List:', colors)

# change the first item to 'Purple'
colors[2] = 'Purple'

# change the third item to 'Blue'
colors[2] = 'Blue'

print('Updated List:', colors)

Output

Original List: ['Red', 'Black', 'Green']
Updated List: ['Purple', 'Black', 'Blue']

Here, we have replaced

• the element at index 0 to 'Purple'
• the element at index 2 to 'Blue'

Remove an Item From a List

We can remove the specified item from a list using the remove() method. For example,

numbers = [2,4,7,9]

# remove 4 from the list
numbers.remove(4)

print(numbers) 

Output

[2, 7, 9]

Remove One or More Elements of a List

Instead of using the remove() method, we can delete an item from a list using the del statement. The del statement can also be used to delete multiple elements or even the entire list.

names = ['John', 'Eva', 'Laura', 'Nick', 'Jack']

# delete the item at index 1
del names[1]
print(names)

# delete items from index 1 to index 2
del names[1: 3]
print(names)

# delete the entire list
del names

# Error! List doesn't exist.
print(names)

Output

['John', 'Laura', 'Nick', 'Jack']
['John', 'Jack']
Traceback (most recent call last):
  File "", line 15, in 
NameError: name 'names' is not defined

Python List Length

To find the number of elements (length) of a list, we can use the built-in len() function. For example,

cars = ['BMW', 'Mercedes', 'Tesla']

print('Total Elements:', len(cars))

Output

Total Elements: 3

Iterating Through a List

We can use a for loop to iterate over the elements of a list. For example,

fruits = ['apple', 'banana', 'orange']

# iterate through the list
for fruit in fruits:
    print(fruit)

Output

apple
banana
orange

Python List Methods

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

Also Read

• Python list() - Convert other datatypes to list.
• Python list comprehension - A concise way to create a list from another sequence in a single line.
• Python enumerate() function - Adds a counter (index by default) to a list.