Finding the length of an array in Python means determining how many elements are present in the array. For example, given an array like [1, 2, 3, 4, 5], you might want to calculate the length, which is 5. Let's explore different methods to efficiently.

Using len()

len() function is the most efficient way to get the number of elements in a list. It's implemented in C internally and returns the length in constant time.

a = [1, 2, 3, 4, 5]
res= len(a)
print(res)

5

Explanation: len(a) to count the number of elements in the list a, stores the result in res.

Using sum()

This method counts each element by summing 1 for every item in the list using a generator expression. It’s useful for iterables when you can’t use len().

a = [1, 2, 3, 4, 5]
res= sum(1 for _ in a)
print(res)

5

Explanation: sum(1 for _ in a) add 1 for each element in the list a, effectively counting the total number of items.

Using For loop

You manually loop through each element and increment a counter variable. While simple and readable, it’s not as concise as built-in functions.

a = [1, 2, 3, 4, 5]

res = 0
for _ in a:
    res += 1
print(res)

5

Explanation: This code sets res to 0 and increments it by 1 for each item in the list a, counting the total elements.

Using enumerate()

The enumerate() function adds a counter to the iterable. You can get the length by capturing the last index it provides. You must start from 1 to match the actual count.

a = [1, 2, 3, 4, 5]

for i, _ in enumerate(a, 1):
    pass
res = i
print(res)

5

Explanation: enumerate(a, 1) loop through the list a with a counter starting at 1. Although the loop does nothing (pass), the final value of i gives the total number of elements.

What is the Difference Between a Python Array and a List?

Let's understand the difference between a Python Array and a List. Both store collections of items but differ in data type, memory efficiency, operations and performance. Knowing these differences helps you choose the right structure based on your needs.

Related Articles

• len()
• sum()
• for loop()
• enumerate()