Lists in Python

This is an introduction to Lists in Python. In this tutorial, we will learn what lists are, how elements are stored in a list, how to create a list, initialize list with elements, how to access the elements in a list, etc., with examples.

Python Lists

Python List is an ordered collection of elements and you can store objects of any datatype in the list.

As Python List is an ordered collection, you can access the elements using index (position of the element in the element). Like in other programming languages like Java, C, C++, etc, the index starts from 0 until the number of items in the list.

Create an empty List

To create an empty list in Python, use list() constructor.

aList = list()

Or you can also use empty square brackets as shown below.

aList = []

Initialize a List

To initialize a list in Python, assign comma separated elements, enclosed in squared bracket to a variable.

aList = [21, 'John', 541, 84.25, True]

In addition, let us find out datatype of the variable aList programmatically using type() function.

Python Program

aList = [21, 'John', 541, 84.25, True]
print(type(aList))

Run the program, and Python interpreter shall print the datatype of aList to standard output.

Output

<class 'list'>

Access elements in a List

To access elements of a list in Python, use variable name followed by square brackets, and the index inside the square brackets. An example is provided below.

element = aList[index]

We already know that index starts from 0. Therefore, aList[0] fetches first element of the list and aList[5] fetches 6th element in the list.

Python Program

aList = [21, 'John', 541, 84.25, True]

element = aList[2]
print(element)

element = aList[4]
print(element)

Output

541
True

aList[2] returns third element of the list and aList[4] returns fifth element of the list.

Modify element in a List

You can change the value of element at a given index by assigning the value to the element using index.

 aList[index] = new_value

In the following program, we shall modify the element present at the index 2.

Python Program

aList = ['apple', 'banana', 'cherry', 'orange', 'papaya']

aList[2] = 'mango'

for element in aList:
    print(element)

Output

apple
banana
mango
orange
papaya

Check if given element is present in List

To check if given element is present in the Python list, you can use in keyword. The syntax to check if element is in list is

element in aList

The above expression returns a boolean value. True if element is present in the list and false if not.

Python Program

aList = ['apple', 'banana', 'cherry', 'orange', 'papaya']

element = 'banana'
if element in aList:
    print('The element is present in list.')
else:
    print('The element is not present in list.')

Output

The element is present in list.

Length of List

You can use len() function to get the length of the list. Pass the list as argument to len() builtin function, and it returns an integer.

Python Program

aList = [21, 541, 84.25]
print(len(aList))

Output

3

Append element to List

list.append() function appends element to the end of the list.

Python Program

aList = [21, 53, 84]
aList.append(96)
print(aList)

Output

3

Insert element in List

list.insert(index, element) method inserts the element at specified index of the list. The index of elements that were originally present from that index are shifted right by one position.

Python Program

aList = ['apple', 'banana', 'cherry']

aList.insert(2, 'mango')

for element in aList:
    print(element)

Output

apple
banana
mango
cherry

Iterate over List elements

You can use any looping technique to iterate over elements of a Python list. Let us go through examples with each of the looping technique.

In the following is a program, we will use Python For loop to iterate over list. We are just printing the element, buy you may write multiple statement to process or transform the list element.

Python Program

aList = [21, 53, 84]

for element in aList:
    print(element)

Output

21
53
84

In the following is a program, we will use Python While loop to iterate over list.

Python Program

aList = [21, 53, 84]

index = 0
while index < len(aList):
    print(aList[index])
    index += 1

Output

21
53
84

Sort a List

list.sort() function sorts the list in ascending order by default. You can specify to sort in descending order using ‘reverse’ attribute.

In the following program, we will sort the list of numbers in ascending order.

Python Program

aList = [21, 53, 84, 5, 62]

aList.sort()

for element in aList:
    print(element)

Output

5
21
53
62
84

In the following program, we will sort the list of numbers in descending order.

Python Program

aList = [21, 53, 84, 5, 62]

aList.sort(reverse=True)

for element in aList:
    print(element)

Output

84
62
53
21
5

Conclusion

In this Python Tutorial, we learned about List in Python programming, how to access its elements and some of the operations that can be performed on a List.