How to Find Length of List in Python?

Lists are flexible data structures that make it possible to keep a group of items. They can store numbers, lines, and even things that are more complicated. But what if you want to count the number of items in a list? That’s why it’s important to determine how long the list is.

In this guide, we’ll learn different ways to find out how long a list is easily. Whether you’re a beginner or an experienced programmer, join me as we unravel the simplicity of Python’s built-in functions and techniques to get the length of any list in no time.

In this article, we will learn how to find the length of list in python programming in the following sequence:

• List in Python
• How to find the Length of List in Python?
  • Len() Method
  • Naive Method

List in Python

A list in Python is implemented to store the sequence of various types of data. However, there are six data types in Python that are capable of storing the sequences but the most common and reliable type is a list. To learn more about python you can join our Master Python programming course.

A list is defined as a collection of values or items of different types. The items in the list are separated with a comma (,) and enclosed with the square brackets [].

It is defined as follows:

list1 = ['edureka', 'python', 2019];
list2 = [1, 2, 3, 4, 5 ];
list3 = ["a", "b", "c", "d"];

Prerequisites needed to get the length of list in Python

1. Using __len__() special function
2. Using len() method
3. Naïve method
4. Find python list length with len()

How to Find the Length of List in Python?

There are two most commonly used and basic methods that are used to find the length of the list in Python:

• Len() Method
• Naive Method

Method 1: By Using Len() Method

There is a built-in function called len() for getting the total number of items in a list, tuple, arrays, dictionary, etc. The len() method takes an argument where you may provide a list and it returns the length of the given list.

The len() method is one of the most used and convenient ways to find the length of list in Python. This is the most conventional technique adopted by all the programmers today.

Syntax:

len(list)

The List parameter is a list for which the number of elements are to be counted. It returns the number of elements in the list.

Example:

ListName = ["Hello", "Edureka", 1, 2, 3]
print ("Number of items in the list = ", len(ListName))

Output:5

Method 2: By Using Naive Counter Method

The len() method is the most commonly used method to find the length of the list in Python. But there is another basic method that provides the length of the list.

In the Naive method, one just runs a loop and increases the counter until the last element of the list to know its count. This is the most basic strategy that can be used in the absence of other efficient techniques.

Example:

ListName = [ "Hello", "Edureka", 1,2,3 ]
print ("The list is : " + str(ListName))
counter = 0
for i in ListName:
counter = counter + 1
print ("Length of list using naive method is : " + str(counter))

Output:

The list is : ["Hello", "Edureka", 1,2,3]
Length of list using naive method is : 5

The len() function is the most time-efficient way to determine a list’s size, although there are alternative ways to do it in Python, such as the length_hint() method.

Method 3: length_hint() method

The length_hint() function is a less known way of getting the length of a list and other iterables. length_hint() is defined in the operator module, so you need to import it from there before you can use it. The syntax for using the length_hint() method is
Python
length_hint(listName)

For example, the following code will get the length of the list my_list:

[Python]
from operator import length_hint

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

length = length_hint(my_list)

print(length)

[/python]

This will print the output 5, which is the length of the list my_list.
The length_hint() function is not as reliable as the len() function, because it does not always return the exact number of items in the list. However, it can be useful in some cases, such as when you need to get an estimate of the length of a list without actually iterating through it.

Method 4: for loop method

This method provides a less practical but still informative way of finding a list’s length with no special method. Getting the length of a list using a Python for loop is also known as the naive method, and can easily be generalized to almost any other programming language.

Example-

count = 0  # Initialize a counter variable

for element in my_list:

    count += 1  # Increment the counter for each element in the list

print(“Length of the list is:”, count)

Output-

Length of the list is: 5

Method 5: Sum() method

Sum() is an inbuilt function that sums up the numbers in the list. It is mainly used to reduce code length and programmer time.

Syntax: sum(iterable,start)

Example-

num = [1,2,4,5]

Sum = sum(num)

print(Sum)

Sum = sum(num, 10)

print(Sum)

Output-

12

22

Method 6: List Comprehension method

List comprehension in Python is a concise way to create lists using a single line of code by specifying an expression followed by a for loop and an optional condition. It provides a more readable and compact alternative to traditional for loops for generating lists.

Example-

numbers = [18, 10, 11,] 

doubled = [x *2 for x in numbers] 

print(doubled)

Output-

[36, 20, 22]

Method 7: Recursion method

In Python, recursion is a method whereby a function calls itself to provide solutions to smaller instances of similar problems. It includes the base case, which ends the recursion, and the recursive case, which reduces the problem into smaller sub-problems. This approach is often used for tasks that can be naturally divided into similar sub-tasks, such as calculating factorials or traversing trees.

Syntax-

def func(): 

              |

              | (recursive call)

              |

    func() —-

Example-

def factorial(n):

    # Base case: if n is 1 or 0, return 1

    if n == 1 or n == 0:

        return 1

    # Recursive case: n * factorial of (n-1)

    else:

        return n * factorial(n – 1)

# Test the function

result = factorial(5)

print(result)

Output-

120

Method 8: Enumerate() function

enumerate() in Python is a built-in function that adds a counter to an iterable, returning it as an enumerate object. This object produces pairs containing an index and the corresponding item from the iterable, making it useful for obtaining both the index and value in loops. It’s commonly used in for loops to track the position of elements in a list or other iterable.

Syntax:

enumerate(iterable,,start=0)

Example-

fruits = [‘apple’, ‘banana’, ‘cherry’]

for index, fruit in enumerate(fruits):

    print(f”Index: {index}, Fruit: {fruit}”)

Output-

Index: 0, Fruit: apple

Index: 1, Fruit: banana

Index: 2, Fruit: cherry

Method 9: Collections module

The Python collections module provides additional special container data types beyond the built-in types available from lists, dictionaries, and tuples. These also include namedtuples to create tuple subclasses with named fields, deque for double-ended queues, Counter for counting hashable objects, and defaultdict for dictionaries that have default values for missing keys. These collections offer enhanced functionality and optimized performance for specific use cases.

Example-

from collections import Counter

# List of items

items = [‘apple’, ‘banana’, ‘apple’, ‘orange’, ‘banana’, ‘apple’]

# Create a Counter object

item_counts = Counter(items)

# Print the counts of each item

print(item_counts)

Output-

Counter({‘apple’: 3, ‘banana’: 2, ‘orange’: 1})

This was all about finding the length of list in Python. The most common approach to determining a string’s length is to use the len() function, however the Naive Method and length_hint() are also acceptable alternatives. This brings us to the conclusion of our article. I hope you now know how to determine the size of a Python list.

With this, we have come to the end of our article. I hope you understood how to find the length of any list in Python.

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