How to Check If a Set Has a Certain Size in Python

Introduction

In this lab, you will learn how to check if a set has a certain size in Python. The lab focuses on using the len() function to determine the number of elements in a set, which is essential for various programming tasks.

You will start by creating a set of numbers and strings in a Python script and then use the len() function to find the size of the set. Finally, you will compare the size of the set with a desired size to check if they match.

Skills Graph

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Understand Set Size

In this step, you will learn how to determine the number of elements in a set using the len() function. Understanding the size of a set is crucial for various programming tasks, such as checking if a set is empty or comparing the sizes of different sets.

First, let's create a simple set in a Python script. Open your VS Code editor in the LabEx environment and create a new file named set_size.py in the ~/project directory.

## Create a set of numbers
my_set = {1, 2, 3, 4, 5}

## Print the set
print(my_set)

Save the file. Now, let's run this script to see the output. Open the terminal in VS Code (you can find it in the bottom panel) and navigate to the ~/project directory (you should already be there by default). Execute the script using the following command:

python set_size.py

You should see the following output:

{1, 2, 3, 4, 5}

Now that we have a set, let's find out how many elements it contains. Add the following lines to your set_size.py script:

## Create a set of numbers
my_set = {1, 2, 3, 4, 5}

## Print the set
print(my_set)

## Get the size of the set using the len() function
set_size = len(my_set)

## Print the size of the set
print("The size of the set is:", set_size)

Save the changes and run the script again:

python set_size.py

This time, you should see the following output:

{1, 2, 3, 4, 5}
The size of the set is: 5

The len() function returns the number of elements in the set. In this case, our set my_set contains 5 elements.

Let's try another example with a set of strings. Modify your set_size.py script to the following:

## Create a set of strings
my_set = {"apple", "banana", "cherry"}

## Print the set
print(my_set)

## Get the size of the set using the len() function
set_size = len(my_set)

## Print the size of the set
print("The size of the set is:", set_size)

Save the file and run it:

python set_size.py

You should see the following output:

{'cherry', 'banana', 'apple'}
The size of the set is: 3

As you can see, the len() function works with sets containing different types of data.

Use len() Function

In the previous step, you learned how to get the size of a set using the len() function. In this step, we will explore more advanced ways to use the len() function with sets, including using it within conditional statements and loops.

Let's start by modifying our set_size.py script to include a conditional statement that checks if the set is empty. Open your set_size.py file in the VS Code editor and modify it as follows:

## Create a set of numbers
my_set = {1, 2, 3, 4, 5}

## Print the set
print(my_set)

## Get the size of the set using the len() function
set_size = len(my_set)

## Print the size of the set
print("The size of the set is:", set_size)

## Check if the set is empty
if set_size == 0:
    print("The set is empty.")
else:
    print("The set is not empty.")

Save the file and run it:

python set_size.py

You should see the following output:

{1, 2, 3, 4, 5}
The size of the set is: 5
The set is not empty.

Now, let's modify the script to create an empty set and check its size. Change the first line of your set_size.py script to create an empty set:

## Create an empty set
my_set = set()

## Print the set
print(my_set)

## Get the size of the set using the len() function
set_size = len(my_set)

## Print the size of the set
print("The size of the set is:", set_size)

## Check if the set is empty
if set_size == 0:
    print("The set is empty.")
else:
    print("The set is not empty.")

Save the file and run it again:

python set_size.py

This time, you should see the following output:

set()
The size of the set is: 0
The set is empty.

As you can see, the len() function returns 0 for an empty set, and our conditional statement correctly identifies that the set is empty.

Now, let's use the len() function in a loop. Suppose we want to remove elements from a set until it is empty. Modify your set_size.py script as follows:

## Create a set of numbers
my_set = {1, 2, 3, 4, 5}

## Print the set
print(my_set)

## Remove elements from the set until it is empty
while len(my_set) > 0:
    ## Remove an arbitrary element from the set
    element = my_set.pop()
    print("Removed element:", element)
    print("The set is now:", my_set)

print("The set is now empty.")

Save the file and run it:

python set_size.py

You should see output similar to the following (the order of removed elements may vary):

{1, 2, 3, 4, 5}
Removed element: 1
The set is now: {2, 3, 4, 5}
Removed element: 2
The set is now: {3, 4, 5}
Removed element: 3
The set is now: {4, 5}
Removed element: 4
The set is now: {5}
Removed element: 5
The set is now: set()
The set is now empty.

In this example, we use the len() function to check if the set is empty in each iteration of the while loop. The pop() method removes an arbitrary element from the set. The loop continues until the set is empty.

Compare with Desired Size

In this step, you will learn how to compare the size of a set with a desired size using conditional statements. This is useful when you need to ensure that a set contains a specific number of elements before performing certain operations.

Let's modify our set_size.py script to compare the size of a set with a desired size. Open your set_size.py file in the VS Code editor and modify it as follows:

## Create a set of numbers
my_set = {1, 2, 3}

## Print the set
print(my_set)

## Get the size of the set using the len() function
set_size = len(my_set)

## Print the size of the set
print("The size of the set is:", set_size)

## Define the desired size
desired_size = 5

## Compare the size of the set with the desired size
if set_size == desired_size:
    print("The set has the desired size.")
elif set_size < desired_size:
    print("The set is smaller than the desired size.")
else:
    print("The set is larger than the desired size.")

Save the file and run it:

python set_size.py

You should see the following output:

{1, 2, 3}
The size of the set is: 3
The set is smaller than the desired size.

Now, let's modify the script to create a set with the desired size. Change the first line of your set_size.py script to create a set with 5 elements:

## Create a set of numbers
my_set = {1, 2, 3, 4, 5}

## Print the set
print(my_set)

## Get the size of the set using the len() function
set_size = len(my_set)

## Print the size of the set
print("The size of the set is:", set_size)

## Define the desired size
desired_size = 5

## Compare the size of the set with the desired size
if set_size == desired_size:
    print("The set has the desired size.")
elif set_size < desired_size:
    print("The set is smaller than the desired size.")
else:
    print("The set is larger than the desired size.")

Save the file and run it again:

python set_size.py

This time, you should see the following output:

{1, 2, 3, 4, 5}
The size of the set is: 5
The set has the desired size.

Finally, let's modify the script to create a set larger than the desired size. Change the first line of your set_size.py script to create a set with 7 elements:

## Create a set of numbers
my_set = {1, 2, 3, 4, 5, 6, 7}

## Print the set
print(my_set)

## Get the size of the set using the len() function
set_size = len(my_set)

## Print the size of the set
print("The size of the set is:", set_size)

## Define the desired size
desired_size = 5

## Compare the size of the set with the desired size
if set_size == desired_size:
    print("The set has the desired size.")
elif set_size < desired_size:
    print("The set is smaller than the desired size.")
else:
    print("The set is larger than the desired size.")

Save the file and run it:

python set_size.py

You should see the following output:

{1, 2, 3, 4, 5, 6, 7}
The size of the set is: 7
The set is larger than the desired size.

This demonstrates how to use the len() function to compare the size of a set with a desired size and perform different actions based on the comparison.

Summary

In this lab, you learned how to determine the size of a Python set using the len() function. You created a Python script named set_size.py and populated it with sets containing numbers and strings. The len() function was then used to retrieve the number of elements within each set, demonstrating its application with different data types.

The lab involved creating sets, printing their contents, and then using len() to obtain and print the set's size. This process was repeated with both a set of integers and a set of strings, reinforcing the understanding of how to effectively use the len() function to determine the number of elements in a set.