List Index Method in Python

From this tutorial, you will be learning about Python list Index method. You will see how to use it on sequences with the help of examples.

Note: The syntax used in the below section is for Python 3. You can change it to any other versions of Python.

Python List Index

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List Index Method

The Index function is a built-in list method that allows you to find out the index or position of an element in a sequence.

In other words, this method searches for an element in the list and returns its index.

Its syntax is as follows:

List_name.index(<element>)

It takes the element as an argument and returns the index. Please note that you can provide any input such as a list or a tuple or a substring.

See the below example.

>>> myList = ['1', '11', 1, 'a', 'x', 1.1]
>>> myList.index(1)
2
>>> myList.index('x')
4

How does the Index() function work?

It takes one input which is the element for which you want the index or position as the output.

This method searches for the element in the list and returns the index matches its value else raises the ValueError error.

While searching for substrings, it raises the following error.

"Substring not found"
>>> first = 'Python is the language of the future.'
>>> print(first.index('lang', 10))
14
>>> print(first.index('invalid', 10))
Traceback (most recent call last):
File "<pyshell#34>", line 1, in <module>
print(first.index('invalid', 10))
ValueError: substring not found
>>>

The flowcharts below attempt to explain it in a diagram:

For elements in the list:

Python List Index Method Flowchart for List element

For characters in the string:

Python List Index Method Flowchart for Substring

Program Examples

Using the wrong element

myList = [2,3,4,5,6]

myList.index(1)

The output is:

Traceback (most recent call last):
File "C:\Python\Python35\test.py", line 3, in <module>
myList.index(1)
ValueError: 1 is not in list

Find the element index in a tuple

myList = [2,3,(3,4),5]

print(myList.index((3,4)))

The result is:

2

Best,

TechBeamers