Python List | index method
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Python's list.index(~) method returns the position of the first occurrence of the specified element in a list.
Parameters
1. x | any
The element to search for in the list.
2. start | number | optional
The index position from which to start the search (inclusive). Defaults to 0.
3. end | number | optional
The index position at which to end the search (exclusive). Defaults to length of list (i.e. last index position in list + 1).
Return value
Index position of the first occurrence of the element x in the list.
Examples
Basic usage
To return the index position of the first occurrence of 'koala' in animals list:
animals = ['koala', 'rabbit', 'dog', 'cat', 'koala']animals.index('koala')
0
Note that index positions in Python start at 0 not 1. Therefore we see return value of 0 as 'koala' is the first element in list animals.
ValueError
To return the index position of the first occurrence of 'panda' in animals list:
animals = ['koala', 'rabbit', 'dog', 'cat', 'koala']animals.index('panda')
ValueError: 'panda' is not in list
As 'panda' does not exist in the list animals, a ValueError is raised:
Start parameter
To start the search for 'koala' at index position 1 of animals:
animals = ['koala', 'rabbit', 'dog', 'cat', 'koala']animals.index('koala', 1)
4
4 is returned as 'koala' first occurs at index position 4 (5th element) after index position 1 in animals.
End parameter
To end the search for 'cat' at the third to last element in animals:
animals = ['koala', 'rabbit', 'dog', 'cat', 'koala']animals.index('cat', 0, -2)
ValueError: 'cat' is not in list
The search excludes the element at index position end (in this case -2 (second to last element) which is occupied by element 'cat'). As a result the search ends after checking element at index position -3 ('dog'), which is why a ValueError is thrown.
