Enumerate in Python

enumerate is a built-in function in Python that converts an iterable to an indexed array. It's usually used when it's necessary to work with values and indexes while looping through a list.

first10Primes = [2, 3, 5, 7, 11, 13, 17, 19, 23, 29]

for index, value in enumerate(first10Primes):
    print(index, value)

'''
Output

0 2
1 3
2 5
3 7
4 11
5 13
6 17
7 19
8 23
9 29
'''

If you have some experience with Javascript, you'll notice a similarity in the array methods: forEach, map and filter.

const first10Primes = [2, 3, 5, 7, 11, 13, 17, 19, 23, 29]

first10Primes.forEach((prime, index) => console.log(prime, index))

In Javascript's case, the index comes second.

In other data structures

enumerate also works with sets:

nums = {3, 4, 5}

for index, value in enumerate(nums):
    print(index, value)
'''
Output
0 3
1 4
2 5
'''

tuples:

nums = (3, 4, 5)

for index, value in enumerate(nums):
    print(index, value)

'''
Output
0 3
1 4
2 5
'''

and dictionaries:

fruit = {"apples": 3, "oranges": 4, "mangoes": 5}

for index, value in enumerate(fruit):
    print(index, value)
'''
Output
0 apples
1 oranges
2 mangoes
'''

It doesn't look useful on dictionaries.

Use cases

enumerate can help you if you find yourself in a situation which requires both indexes and items. It has the same time complexity as list lookup: O(n), so you have nothing to worry.

Thanks for reading. Adios ✌🏾🧡.