Python List index()

2021 VietMX PYTHON 0

In this tutorial, we will learn about the Python List index() method with the help of examples.

The index() method returns the index of the specified element in the list.

Example

animals = ['cat', 'dog', 'rabbit', 'horse']

# get the index of 'dog'
index = animals.index('dog')


print(index)

# Output: 1

1. Syntax of List index()

The syntax of the list index() method is:

list.index(element, start, end)

2. list index() parameters

The list index() method can take a maximum of three arguments:

  • element – the element to be searched
  • start (optional) – start searching from this index
  • end (optional) – search the element up to this index

3. Return Value from List index()

  • The index() method returns the index of the given element in the list.
  • If the element is not found, a ValueError exception is raised.

Note: The index() method only returns the first occurrence of the matching element.

4. Example 1: Find the index of the element

# vowels list
vowels = ['a', 'e', 'i', 'o', 'i', 'u']

# index of 'e' in vowels
index = vowels.index('e')

print('The index of e:', index)

# element 'i' is searched
# index of the first 'i' is returned
index = vowels.index('i')


print('The index of i:', index)

Output

The index of e: 1
The index of i: 2

5. Example 2: Index of the Element not Present in the List

# vowels list
vowels = ['a', 'e', 'i', 'o', 'u']

# index of 'p' is vowels
index = vowels.index('p')

print('The index of p:', index)

Output

ValueError: 'p' is not in list

6. Example 3: Working of index() With Start and End Parameters

# alphabets list
alphabets = ['a', 'e', 'i', 'o', 'g', 'l', 'i', 'u']

# index of 'i' in alphabets
index = alphabets.index('e')   # 1

print('The index of e:', index)

# 'i' after the 4th index is searched
index = alphabets.index('i', 4)   # 6

print('The index of i:', index)

# 'i' between 3rd and 5th index is searched
index = alphabets.index('i', 3, 5)   # Error!

print('The index of i:', index)

Output

The index of e: 1
The index of i: 6
Traceback (most recent call last):
  File "*lt;string>", line 13, in 
ValueError: 'i' is not in list

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