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))Try Online
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)Try Online
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) Try Online 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.') Try Online 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))Try Online
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)Try Online
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) Try Online 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) Try Online 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 Try Online 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) Try Online 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) Try Online 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.