## Python Find Index of all Occurrences in List

Last Updated On Friday 22nd Apr 2022

## Python Find Index of all Occurrences in List

### List Comprehension

List comprehension offers a shorter syntax when you want to create a new list based on the values of an existing list.

• The number of occurrences of an element in a list can be calculated with the help of list.count(<item>).
• It takes the item to be counted as its argument and returns the total number of times that element appears in the list.

### count()

The count() method returns the number of occurrences of a substring in the given string.

### Syntax

	string.count(substring, start=..., end=...)


	items = [1, 4, 7, 8, 2, 9, 2, 1, 1, 0, 4, 3]

print(items.count(1)) # 3



### Finding the index of items

• <list>.index(<item>) will return the index number of the first occurrence of an item passed in.

### Find all Indices of Element in list Python

	items = [7, 4, 1, 0, 2, 5]

print(items.index(4)) # 1

print(items.index(10)) # ValueError: 10 is not in list


• start and end indices can also be provided to narrow the search to a specific section of the list.
	names = ["Adam", "Alice", "Ben", "Tom", "Sam", "Jane"]

names.index("Ben", 2, 5) # 3


• You can use enumerate() in a loop in almost the same way that you use the original iterable object.
	names = ["Adam", "Alice", "Ben", "Tom", "Sam", "Jane"]

indices = [i for i, x in enumerate(names) if x == "Tom"]

print(indices) # 


	import numpy as np
values = np.array([ 11,22,33,12,23,45,54,56,23,82,11 ])

print(np.where(values == 11)) # [ 0 10 ]