Python List index() Method

The List index() method finds the position of the first occurrence of the given element in the list.

If specified item is not found, it raises ValueError exception.

Syntax

my_list.index(item, start, end)

index() Parameters

Python List index() method parameters::

index() Return Value

Python List index() method returns the index of the given element in the list.

Examples

Example 1: Find the index of an element

For example, find the index of Anna in a list:

my_list = ['Ryan', 'Tom', 'Anna', 'David']
index = my_list.index('Anna')
print(index) # Output: 2

output

2

Example 2: Find the index of an element when there are duplicates

If the list has many instances of the specified item, the index() method returns only the index of first instance.

For example, find first occurrence of character d:

my_list = ['a','d','c','d','b','c','d','e','f','d','f','a']
index = my_list.index('d')

print(index) # Output: 1

output

1

Example 3: index() on Item that does Not Exist

The index() method raises a ValueError if specified item is not found in the list.

my_list = ['Tom', 'Ryan', 'David']
print(my_list.index('Anna')) # Raises ValueError: 'Anna' is not in list

output

Traceback (most recent call last):
  File "main.py", line 2, in <module>
    print(my_list.index('Anna')) # Raises ValueError: 'Anna' is not in list
ValueError: 'Anna' is not in list

To avoid such exception, you can check if item exists in a list, using in operator inside if statement.

my_list = ['Tom', 'Ryan', 'David']
if 'Anna' in my_list: # check if exists in my_list before index()
    print(my_list.index('Anna'))

Example 4: Limit index() Search to Subsequence with start and end parameters

If you want to search the list not starting from the beginning, you have to specify the start parameter. Similarly, you can also specify where to stop the search with end parameter.

my_list = [0, 1, 2, 3, 4, 5, 4, 3, 2, 1, 0]

index = my_list.index(3)       
print(index) # Output: 3

index_with_start = my_list.index(3, 4)
print(index_with_start) # Output: 7

index_with_start_end = my_list.index(3, 4, 6) 
print(index_with_start_end) # Raises ValueError

output

3
7
Traceback (most recent call last):
  File "main.py", line 12, in <module>
    index_with_start_end = my_list.index(3, 4, 6) 
ValueError: 3 is not in list

Example 5: Finding All Occurrences with index() and List Comprehension

You can use List Comprehension and enumerate built-in function to return a list of all indexes where the specified item occurs in the list or string.

def find_all_indexes(item, list_or_string):
    return [n for n, item_in_list in enumerate(list_or_string) if item_in_list == item]

print(find_all_indexes('banana', ['apple', 'banana', 'cherry', 'banana', 'date']))

output

[1, 3]