Find Size of a List in Python

What Is a List in Python?

A list in Python is a collection data type used to store several values using a single variable. The values in the list may or may not be of the same type. However, it is usually used to store values of the same type, which represent some collection. It can also store duplicate values. A list is ordered and changeable and is represented by writing values separated by commas, stored within square brackets as shown below.

listOfOdd=[1, 3, 5, 7, 9]

listOfChar=[‘a’, ‘b’, ‘c’, ‘d’]

listOfMix=[‘a’, ‘b’, 1, 3]

The len() Function in Python

len() is a built-in function in Python that returns the length of an object like a list, string, dictionary, set, tuple, etc. The len() function takes one argument: an object which may be a sequence or a collection, and returns an integer, which is the number of items in the object, i.e., its size. len() performs this operation in O(1) time.

Syntax:

len(object)

Example:

listEx = [1, 2, 3, ‘a’,’b’,’c’]

stringEx=’InterviewKickstart’

setEx={0,2,4,6,8}

tupleEx=(0,’Zero’,1,’One’)

dictionaryEx={‘Zero’: 0, ‘One’:1, ‘Two’:2}

print(len(listEx))

print(len(stringEx))

print(len(setEx))

print(len(tupleEx))

print(len(dictionaryEx))

Output:

6

18

5

4

3

Finding the Size of a List Using len() Function

The most commonly used method of finding the size of a list is using the len() function. The built-in class list also has a method __len__(), which also returns the size/number of items in the list.

The len() function actually works by calling the object’s __len__() method. Since attributes in the format __xyz__ often are more complex than we realize, their direct use isn’t encouraged. Hence we prefer the len() method for finding the size of a list. Let us look at both of these methods through an example.

Example:

Finding The Size of a List Using for Loop

We can also find the size of a list by simply using a for loop, creating a count variable, iterating through all the items in the list, and incrementing the value of count by one in each iteration.

Since this method isn’t very pythonic, we again prefer the len() function for finding the size of a list. We can make use of a for loop to find the length of each element in a list that only stores objects while using the len() function. Let us see how we can use this method through an example.

Example:

FAQs

Question 1: Can we use the len() function in a for loop to find the size of string elements in a list that also contains items that are not objects (like int, char, etc.)?

Example:

listEx = [‘a’,’b’,’c’, 1 ,’Interview’, ‘Kickstart’]

Answer: No. len() takes an object as its argument, and we’ll get a type error since int, char, etc., are not objects.

Question 2: Can we use the len() function in a for loop to find the size of string elements in a list that also contains items that are objects but of different types (like a dictionary, tuple, etc.)

Example:

listEx = [{‘a’:1,’b’:1,’c’:1},’Interview’, ‘Kickstart’]

Answer: Yes. If the list contains elements of different data types, but all are objects that are sequences or collections, we can use the len() function to find the size of each element.

Recommended Reading

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Article contributed by Tanya Shrivastava