How To Find the Length of a List in Python

ByMuhammad Usman Shafique
How To Find the Length of a List in Python

Python is the most powerful and widely used programming language. It has many built-in functions to help developers code easier and faster, Using the built-in function let’s see, How To Find the Length of a List in Python.

There are multiple ways to find the length of a list in Python. We discuss the built-in len() function (example: len(my_list)) and other ways to find the length in various aspects like performance and efficiency

Before moving further, Let’s see what is a list and how it is used

What is a List?

A list is a collection of items enclosed in square brackets and the items are separated by commas. It allows us to store multiple values in a single variable and can be accessed via the index

For example, you can create a list of integers, strings, or even other lists or dictionaries and the values can be accessed via the index, Which will start from 0 -> (length of the list – 1)

Item -> index

a -> 0

b -> 1

c -> 2

d -> 3

e -> 4

f -> 5

Here’s an example:

my_list=[a,b,c,d,e,f]

print (mylist[1])

Output:

b

List can have a mix of different data types and the below methods are still valid for finding the length

my_list=[a,1,c,3,e,4]

There are multiple ways to find the length of a list and below are some of the ways to achieve it

  • Using len()
  • Using lenth_hint()
  •  Using _len_()
  • Using Loop

Using len()

len() function can be used to find the length of a list, for that you can simply pass the list as an argument to the len() function as below. 

Here’s an example:

my_list = [1, 2, 3, 4, 5] 

list_length = len(my_list) 

print("List Size = ",list_length)

Output:

List Size = 5 

In the above example, We have a list with 5 items and it’s a collection of integers. Now to find the length, we pass the list variable to the len() function and it returns the number of items present, In this case, it is 5. 

len() function can be used on other iterable objects as mentioned below

str, bytes, tuple, list, range, dict, set, frozenset

Here’s an example:

Python len() with String

my_string = "Learn and Share" 

string_length = len(my_string) 

print("String Length = ",string_length)

Output:

String Length = 15

In the above example, We can see the len() function returns the number of characters in the string, which is 11.

Similarly, it can be used on different objects

Python len() with Tuples

example_tuple = ()

len(example_tuple)

Output: 0

example_tuple = (1,2,3)

len(example_tuple)

Output: 3

Python len() with Sets

example_set = {}

len(example_set)

Output: 0

example_set= {1,2,3}

len(example_set)

Output: 3

Using length_hint()

We can also use length_hint() method to estimate the length of an iterable object. Basically, it is different from len () function. When the length of an object is known then lenth_hint() will provide you with the exact value else it will give you an estimated value 

For list() the length is always known and the function will give you the exact value

Here’s an example:

my_items = ["apple", "orange", "banana"]

from operator import length_hint

list_len_hint = length_hint(items)

print("List Length = ",list_len_hint)

Output:

List Length = 3

NOTE: For a normal list both len and length_hint will give the same results. But this method is less efficient than using the built-in len() function, but it can still be useful in certain situations. 

When to use length_hint()

One good use case where length_hint() is more useful than len () is when you want to get the length of list-iterator

Here’s an example:

from operator import length_hint 

my_items = ["apple", "orange", "banana"]

len(my_items)

Output: 3 

length_hint(my_items) 

Output: 3 

list_iterator = iter(my_items) 

len(list_iterator)

TypeError: object of type ‘list_iterator’ has no len() 

length_hint(list_iterator) 

Output: 3

Using _len_() function

_len_() is called the magic method, which will return the length of the object in a non-negative integer. len() function is been implemented using _len_() method.

So, When we use len() it internally invoke _len_() to calculate the length

Here’s an example:

my_items = ["apple", "orange", "banana"]

list_Length = my_items._len_()

print("List Length = ", list_Length)

Output

List Length = 6

In the above example, We are using _len_() method to calculate the length of the list, In this case, the output is 6 as same as in other examples

NOTE: Magic methods are not intended to be invoked by us (the user) but the invocation will happen internally from the class on a certain action.

Here’s an example:

len() -> Think of len function as below, Whenever the len is called it will internally invoke _len_ magic method

def len(my_items): 
    return my_items._len_()

Using Loop

We can use LOOP  to find the length of a list in Python. You can use a loop (such as a for loop) to iterate through the list and record a count of the number of items. 

This method is less efficient than using the built-in len() function, but it can still be useful in certain situations. 

Here’s an example:

my_list = [1, 2, 3, 4, 5] 

count = 0 

for item in my_list: 
    count += 1 

print(count)

Output:

5 

Final Thoughts

In conclusion, the len() function is a quick and easy way to find the length of a list or other iterable object in Python. In addition, We have also discussed various other ways to calculate the length of the object and the place where it can probably be used

It’s a useful tool to have in your toolbox, and you’ll likely find yourself using it often in your coding projects.

Good Luck with Your Learning !!

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