python length of list

Python Length of List

The Python Length of List is a collection data type in Python in which we can store our entries. These entries are ordered and can be changed. Python’s len() method helps find the length of an array, object, list, etc. 

To implement the list, you must store a sequence of various types of data in it. There are alternatives to the list, but the most reliable option is a list. The data or elements in the list are separated with a comma (,) and the complete list is surrounded by square brackets []. 

Just like we use indexes to find the specific data in an array, lists can also do this. So, we can use index numbers to find data at any specific position in the list. 

Python list has a length that denotes the total number of items or the size of the list. A list can be defined as a collection of items or data of different types. 

Square brackets can quickly identify a List and the values separated by a comma (,). Len() is a built-in function of Python that returns the total number of items in a list, array, tuple, dictionary, etc. It just takes an argument where you are required to provide a list, and it will return the length of the list that we provided. 

This article will discuss how we can find the length of a list in Python using various methods and some other factors. If you wish to brush up on your basic skills in Python, you can take up the free online Python Fundamentals for Beginners course and enhance your skills.

Let’s get started!

Syntax

The syntax of using the len() function is straightforward, and it doesn’t require any specific type of set as an argument. You may provide an array, tuple, list, or dictionary as an argument. You may even provide the collection of items as a parameter inside the parenthesis. The syntax of declaring a list in Python is as follows:

list_of_items = [item1,item2,item3,….]

The item can be any type of data in the above syntax, such as a string or an integer. But it should be noted that declaring a string data in the list, which should be enclosed in double-quotes while declaring an integer, doesn’t require quotation marks. 

Let us see how you can declare a string data in the list:

String_list = [“string1”, “string2”, “string3”]

Now, let users have a look at how you can declare integer type of data in the list:

Integer_list = [1,2,3,4]

As we already discussed, you could incorporate different kinds of data in a single list. Let us see an example for this scenario too:

Int_stringList = [“string1”, 1, “string3”, 5]

You can also declare empty lists and add data later in the code. To declare an empty list, you may see the reference example below:

Empty_list = []

Examples

There are different cases where we can apply len() method. However, some of the use cases to apply the len() method are discussed in this section. You may see different methods here, such as finding the length without using any predefined function, or we can also use the naïve method and the len() method. We also discussed an example where we are trying to find the time it takes to execute all the code. In this section, we will see some examples for a better understanding of this concept:

Example 1: Finding the length of a list using the naïve method

# here is the python code to find the length of the list in python
# by following the Native method
# we will initialise the list first
list_of_items = [1, 2, 5, 3, 2, 5]
# first, we will print all the items as output
print('The items in the list are: ' + str(list_of_items))
# now, we will initiate a counter that will count the items in our list
# we will use a for loop to go through each element in the list
# in each loop until the last element is encountered
counter = 0
for I in list_of_items:
   counter = counter + 1
   # we incremented by one in the counter to count the number of elements
# converting the data type of counter to string
length_of_list = str(counter)
# printing the total no. of elements as output
print('The length of the list is: ' +  length_of_list)

OUTPUT:

The items in the list are: [1, 2, 5, 3, 2, 5]

The length of the list is: 6

In the above example, we didn’t use any function or method. Instead, we used the naïve method to find the length of any list. We used a loop that traverses through the list and increases the count that returns the total number of elements in the list when the for loop stops. 

Example 2: Using len() method

# initiating an empty list first
list = []
# adding items to the list
list.append('Learn')
list.append('from')
list.append('Great')
list.append('Learning')
list.append('Platform')
# finding the length of the list using the len method
length_of_list = len(list)
# printing the length of the list
print('The length of the list is: ' + str(length_of_list))

OUTPUT: 

The length of the list is: 5

Example 2 (b)

# initiating a list with items in it
list_of_items = ['Great', 'Learning', 'Academy', 'online', 'courses']
# getting the length of the list by using the len method
length_of_list = len(list_of_items)
# printing the length of the list
print('The length of our list is: ', length_of_list)

OUTPUT:

The length of our list is:  5

We discussed two examples, i.e. Example-2 and Example-2(b), where we used len() method. This method is beneficial and an easy way to find the length of the list. Most programmers use this method nowadays to find the length because it is the most conventional technique. 

# in this example, we will demonstrate
# how to find the length of the list by using len and length_hint methods
# we will compare both the methods later in this article
 
# first import the length_hint operator
from operator import length_hint
# now, we will initialise the list with items in it
list_of_items = [1, 3, 5, 7, 9, 11]
# First, we will print the list as an output
print('The list of items is: ' + str(list_of_items))
# now, we are going to find the length using the len method
length_of_list = len(list_of_items)
# now, we are finding the length of the list using the length_hint method
length_hint_method = length_hint(list_of_items)
# Lastly, we will print the length of the list using both 
# the methods
print('The length of the list is: ' + str(length_of_list))
print('The length of the list using length_hint method is: ' + str(length_hint_method))

OUTPUT:

The list of items is: [1, 3, 5, 7, 9, 11]

The length of the list is: 6

The length of the list using the length_hint method is: 6

In the above example, we used a less popular technique, and it is used to find the length of the list. This method (length_hint()) is defined in the operator class of Python, where it is used to tell the number of elements in the list. 

Example 3 (b): Analyzing the performance of the code to find len()

# here, we will analyse the performance of our code
# to find the length of the list
# we are importing the length_hint function
import time
from operator import length_hint
# now, we will initialise our list with items in it
list_of_items = [1, 3, 5, 7, 9, 11]
# first, we will print the list of items as it is
print('The items in the list are: ' + str(list_of_items))
# now, we will find the length of the list
# we will initialise the length as 0
begin_time_constraint = time.time()
length = 0
for I in list_of_items:
   length = length + 1
end_time_constraint = str(time.time() - begin_time_constraint)
# we will find the length of the list using the len method below
begin_time_len = time.time()
length_of_list = len(list_of_items)
end_time_len = str(time.time() - begin_time_len)
# we will also find the length of the list using the lenth_hint method
# to find the time constraint of it
begin_time_hint = time.time()
length_hint_list = length_hint(list_of_items)
end_time_hint = str(time.time() - begin_time_hint)
# now, we will print all the results
print('The time taken by naïve method to calculate the length of the list is: ' + end_time_constraint)
print('The time taken by len method to calculate the length of the list is: ' + end_time_len)
print('The time taken by length_hint method to calculate the length of the list is: ' + end_time_hint)

OUTPUT:

The items in the list are: [1, 3, 5, 7, 9, 11]

The time taken by the naïve method to calculate the length of the list is: 3.0994415283203125e-06.

The time taken by the len method to calculate the length of the list is: 1.1920928955078125e-06

The time taken by the length_hint method to calculate the length of the list is: 4.0531158447265625e-06.

In the above example, we analyzed the time it takes to execute all the code. It’s a best practice to calculate the time complexity of the code as a good programmer. When you start programming and solving problems, you should also consider how much time your code takes to execute all the code and give results. Therefore, we included this example in this article to have a better understanding of an efficient code. 

How to find the Length of the List in Python?

Two possible methods can be applied to find the length of the list. The first method is a len() method which is a built-in function, and len() is most commonly used to find the size of a list. The second method is by applying the logic only. In the second method, you must use your logical skills to get familiar with the concept. 

Let us discuss both these methods to find the length of the list: 

1. Len() Method

Len() is a built-in function in Python that can get the total number of elements in a list, array, dictionary, or tuple. To get the size of the list, you need to provide an argument of the list that will return the length of a given list. 

This function is beneficial, and there are several ways that it enhances our ways of finding the length of a list in Python. The syntax for using Len() function is as below:

Syntax:

len(list)

In the above syntax, the list keyword uses the len() built-in function. And the list is the argument that represents the list. It will return the total number of elements in the list. 

Example:

# initiating a list with items in it
list_of_items = ['Great', 'Learning', 'Academy', 'online', 'courses']
# printing the length of the list using the len method
print('The length of our list is: ', len(list_of_items))

Output:

The length of our list is:  5

The len() method is very easy, and a beginner can also understand this method quickly. In the above example, we initiated a list that added 5 elements, including strings and integers. In the following line, we used the len() method wherein, in parenthesis, we provided the argument of the name of the list. This len() method counts the total number of elements in our list and prints it as output in the above example. 

2. Naive Method

The len() function is very commonly used for finding the total length of the list. But there are other ways to find the size of a list. In this Naïve method, we will use a for loop with a count variable. We will initiate the count variable with 0, and in the loop, when it goes through all the elements in the list, it will increment by one in the count, and when it traverses through all the elements in the list, it will stop the loop and give the final count as output. 

This count will provide the total number of elements in the list. 

Example:

list_of_items = ['Great', 'Learning', 'Academy', 'online', 'courses']
print('The items in our list is: ' + str(list_of_items))
length = 0
for I in list_of_items:
   length += 1
print('The length of the list by using Naïve method is: ', str(length))

OUTPUT: 

The items in our list is: [‘Great’, ‘Learning’, ‘Academy’, ‘online’, ‘courses’]

The length of the list by using the Naïve method is:  5

In the above example, the naïve method doesn’t require any predefined function, class or built-in function. Instead, we used naïve programming, where we used for loop and a variable that counts the total number of elements in the list. 

Is the len() method specific to the list?

No, the len() method takes the argument wherein we can provide list, tuple, string, byte, array, dictionary, etc.) and returns the total number of elements. Therefore, it isn’t specific to the list only. 

We need to provide an argument in the len() method; otherwise, it will throw an error. Therefore, we will provide the list, tuple, array, dictionary, etc., to get the size of the argument we passed inside the parentheses. 

Using the len() function, you can get the total number of elements or the length of the set or frozenset. 

By definition, the argument of the len() method can be an object, e.g. a list, string, tuple, range, dictionary, a collection of items, etc. 

Therefore, we can conclude that the len() method isn’t specific to list only. Instead, we can provide an array, tuple, dictionary, etc., as the argument. We can also provide collection as a parameter in this function. 



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By GIL