How to Check If a Variable Is Not None in Python

Introduction

In this lab, you will learn how to check if a variable is not None in Python. None represents the absence of a value, and understanding how to work with it is crucial for writing robust code.

This lab guides you through exploring non-None values by creating a Python script. You'll assign None to a variable and then check its value using an if statement. Subsequently, you'll assign a non-None value (a string) to the same variable and check its value again, observing the change in output. Finally, you will modify the script to explore different non-None values.

Skills Graph

%%%%{init: {'theme':'neutral'}}%%%% flowchart RL python(("Python")) -.-> python/BasicConceptsGroup(["Basic Concepts"]) python(("Python")) -.-> python/ControlFlowGroup(["Control Flow"]) python/BasicConceptsGroup -.-> python/variables_data_types("Variables and Data Types") python/BasicConceptsGroup -.-> python/booleans("Booleans") python/ControlFlowGroup -.-> python/conditional_statements("Conditional Statements") subgraph Lab Skills python/variables_data_types -.-> lab-559607{{"How to Check If a Variable Is Not None in Python"}} python/booleans -.-> lab-559607{{"How to Check If a Variable Is Not None in Python"}} python/conditional_statements -.-> lab-559607{{"How to Check If a Variable Is Not None in Python"}} end

Explore Non-None Values

In this step, you will learn about None in Python and how to identify values that are not None. None is a special value in Python that represents the absence of a value or a null value. It's often used to indicate that a variable has not been assigned a value or that a function does not return a value.

Understanding how to work with None is crucial for writing robust and error-free Python code. Let's start by creating a Python script to explore non-None values.

Open your VS Code editor.
Create a new file named explore_none.py in the ~/project directory.
Add the following code to the explore_none.py file:

## Assign None to a variable
my_variable = None

## Check if the variable is None
if my_variable is None:
    print("The variable is None")
else:
    print("The variable is not None")

## Assign a non-None value to the variable
my_variable = "Hello, LabEx!"

## Check again if the variable is None
if my_variable is None:
    print("The variable is None")
else:
    print("The variable is not None")

This script first assigns None to the variable my_variable. Then, it uses an if statement to check if my_variable is None. If it is, it prints "The variable is None". Otherwise, it prints "The variable is not None".

Next, the script assigns the string "Hello, LabEx!" to my_variable. It then checks again if my_variable is None. This time, it will print "The variable is not None".

Save the explore_none.py file.
Run the script using the following command in your terminal:

python explore_none.py

You should see the following output:

The variable is None
The variable is not None

This output demonstrates how to check if a variable is None and how the value of a variable can change during the execution of a program.

Now, let's modify the script to explore different non-None values.

Open the explore_none.py file in VS Code.
Modify the script to include the following:

## Assign None to a variable
my_variable = None

## Check if the variable is None
if my_variable is None:
    print("The variable is None")
else:
    print("The variable is not None")

## Assign an integer value to the variable
my_variable = 42

## Check again if the variable is None
if my_variable is None:
    print("The variable is None")
else:
    print("The variable is not None")

## Assign a boolean value to the variable
my_variable = True

## Check again if the variable is None
if my_variable is None:
    print("The variable is None")
else:
    print("The variable is not None")

In this modified script, we assign an integer value (42) and a boolean value (True) to my_variable. Each time, we check if my_variable is None. The output will show that my_variable is not None after each assignment.

Save the explore_none.py file.
Run the script again using the same command:

python explore_none.py

You should see the following output:

The variable is None
The variable is not None
The variable is not None

This exercise demonstrates that None is a specific value and that any other value, including integers, strings, and booleans, is considered a non-None value. Understanding this distinction is essential for writing conditional statements and handling different types of data in Python.

Use the is not Operator

In the previous step, you learned how to check if a variable is None using the is operator. In this step, you will learn how to use the is not operator to check if a variable is not None. The is not operator is the logical opposite of the is operator.

Let's modify the explore_none.py script from the previous step to use the is not operator.

Open the explore_none.py file in VS Code.
Modify the script to use the is not operator as follows:

## Assign None to a variable
my_variable = None

## Check if the variable is not None
if my_variable is not None:
    print("The variable is not None")
else:
    print("The variable is None")

## Assign a non-None value to the variable
my_variable = "Hello, LabEx!"

## Check again if the variable is not None
if my_variable is not None:
    print("The variable is not None")
else:
    print("The variable is None")

In this modified script, the if statements now use the is not operator to check if my_variable is not None. The logic is reversed: if my_variable is not None, it prints "The variable is not None"; otherwise, it prints "The variable is None".

Save the explore_none.py file.
Run the script using the following command in your terminal:

python explore_none.py

You should see the following output:

The variable is None
The variable is not None

The output is the same as in the previous step, but the logic used to achieve it is different. The is not operator provides a more direct way to check for non-None values.

Now, let's add more examples to the script to solidify your understanding of the is not operator.

Open the explore_none.py file in VS Code.
Modify the script to include the following:

## Assign None to a variable
my_variable = None

## Check if the variable is not None
if my_variable is not None:
    print("The variable is not None")
else:
    print("The variable is None")

## Assign an integer value to the variable
my_variable = 42

## Check again if the variable is not None
if my_variable is not None:
    print("The variable is not None")
else:
    print("The variable is None")

## Assign a boolean value to the variable
my_variable = True

## Check again if the variable is not None
if my_variable is not None:
    print("The variable is not None")
else:
    print("The variable is None")

This script now includes checks for an integer and a boolean value using the is not operator.

Save the explore_none.py file.
Run the script again using the same command:

python explore_none.py

You should see the following output:

The variable is None
The variable is not None
The variable is not None

This exercise reinforces the concept that the is not operator is used to check if a variable does not have the value None. It's a useful tool for writing concise and readable code when dealing with potentially missing or uninitialized values.

Combine with Simple Conditions

In this step, you will learn how to combine the is not operator with other simple conditions using logical operators like and and or. This allows you to create more complex conditional statements that check for multiple conditions at once.

Let's start by modifying the explore_none.py script to include additional conditions.

Open the explore_none.py file in VS Code.
Modify the script to include the following:

## Assign None to a variable
my_variable = None
my_number = 10

## Check if the variable is not None and the number is greater than 5
if my_variable is not None and my_number > 5:
    print("The variable is not None and the number is greater than 5")
else:
    print("One or both conditions are not met")

## Assign a non-None value to the variable
my_variable = "Hello, LabEx!"

## Check again if the variable is not None and the number is greater than 5
if my_variable is not None and my_number > 5:
    print("The variable is not None and the number is greater than 5")
else:
    print("One or both conditions are not met")

In this script, we've introduced a new variable my_number and set it to 10. The if statements now check two conditions: whether my_variable is not None and whether my_number is greater than 5. The and operator ensures that both conditions must be true for the if block to be executed.

Save the explore_none.py file.
Run the script using the following command in your terminal:

python explore_none.py

You should see the following output:

One or both conditions are not met
The variable is not None and the number is greater than 5

The first if statement fails because my_variable is None. The second if statement succeeds because my_variable is not None and my_number is greater than 5.

Now, let's explore the or operator.

Open the explore_none.py file in VS Code.
Modify the script to use the or operator as follows:

## Assign None to a variable
my_variable = None
my_number = 10

## Check if the variable is not None or the number is greater than 5
if my_variable is not None or my_number > 5:
    print("At least one condition is met")
else:
    print("Neither condition is met")

## Assign a non-None value to the variable
my_variable = "Hello, LabEx!"

## Check again if the variable is not None or the number is greater than 5
if my_variable is not None or my_number > 5:
    print("At least one condition is met")
else:
    print("Neither condition is met")

In this modified script, the if statements now use the or operator. This means that the if block will be executed if at least one of the conditions is true.

Save the explore_none.py file.
Run the script again using the same command:

python explore_none.py

You should see the following output:

At least one condition is met
At least one condition is met

The first if statement succeeds because my_number is greater than 5, even though my_variable is None. The second if statement also succeeds because both conditions are true.

This exercise demonstrates how to combine the is not operator with other simple conditions using logical operators. This allows you to create more complex and flexible conditional statements in your Python code.

Summary

In this lab, the initial step focuses on understanding None in Python and how to identify non-None values. A Python script named explore_none.py is created to demonstrate this. The script assigns None to a variable and uses an if statement with the is operator to check if the variable is None, printing the corresponding message. Subsequently, the variable is assigned a string value, and the same check is performed, illustrating how the variable's value affects the output.

The script is then executed, and the output confirms the expected behavior: first, "The variable is None" is printed, followed by "The variable is not None". This demonstrates the fundamental concept of checking for None values and how a variable's value can change during program execution. The lab then proceeds to modify the script for further exploration of non-None values.