How to Check If a Condition Is True in Python

Introduction

In this lab, you will learn how to check if a condition is true in Python using Boolean conditions and comparison operators. This is fundamental for decision-making in programming.

You'll start by understanding Boolean values (True and False) and common comparison operators like ==, !=, >, <, >=, and <=. You'll then implement an if statement (covered in subsequent steps, but implied by the need to check conditions). Finally, you'll learn how to combine multiple conditions using and and or operators (also covered in subsequent steps). You'll practice these concepts by creating and running a Python script that compares variables and prints the resulting Boolean values.

Skills Graph

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Understand Boolean Conditions

In this step, you will learn about Boolean conditions in Python. Boolean conditions are expressions that evaluate to either True or False. They are fundamental to decision-making in programming, allowing your code to execute different blocks of code based on whether a condition is true or false.

Let's start by exploring the basic Boolean values:

True
False

These are keywords in Python and must be capitalized.

Now, let's look at some common comparison operators that produce Boolean values:

== (equal to)
!= (not equal to)
> (greater than)
< (less than)
>= (greater than or equal to)
<= (less than or equal to)

To practice using these operators, you will create a Python script named conditions.py in your ~/project directory using the VS Code editor.

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

x = 5
y = 10

print("x == y:", x == y)
print("x != y:", x != y)
print("x > y:", x > y)
print("x < y:", x < y)
print("x >= y:", x >= y)
print("x <= y:", x <= y)

This code assigns the values 5 and 10 to the variables x and y, respectively. Then, it uses the comparison operators to compare these variables and prints the resulting Boolean values.

To run the script, open your terminal and execute the following command:

python ~/project/conditions.py

You should see the following output:

x == y: False
x != y: True
x > y: False
x < y: True
x >= y: False
x <= y: True

This output shows the result of each comparison. For example, x == y is False because 5 is not equal to 10.

You can also use Boolean operators to combine multiple conditions. The most common Boolean operators are:

and (returns True if both conditions are true)
or (returns True if at least one condition is true)
not (returns the opposite of the condition)

Let's modify the conditions.py script to include Boolean operators.

Open the conditions.py file in VS Code.
Modify the code to include the following:

x = 5
y = 10

print("x > 0 and y < 20:", x > 0 and y < 20)
print("x < 0 or y > 5:", x < 0 or y > 5)
print("not (x == y):", not (x == y))

This code combines multiple conditions using the and, or, and not operators.

Save the changes and run the script again:

python ~/project/conditions.py

You should see the following output:

x > 0 and y < 20: True
x < 0 or y > 5: True
not (x == y): True

This output shows the result of each combined condition. For example, x > 0 and y < 20 is True because both x > 0 and y < 20 are true.

Understanding Boolean conditions and operators is crucial for writing programs that can make decisions based on different inputs and situations. In the next step, you will learn how to use these conditions in if statements to control the flow of your program.

Implement an if Statement

In this step, you will learn how to use if statements in Python to control the flow of your program. An if statement allows you to execute a block of code only if a certain condition is true.

The basic syntax of an if statement is:

if condition:
    ## Code to execute if the condition is true

The condition is a Boolean expression that evaluates to either True or False. If the condition is True, the code inside the indented block is executed. If the condition is False, the code inside the block is skipped.

Let's create a simple example to demonstrate how if statements work. You will modify the conditions.py script you created in the previous step.

Open the conditions.py file in VS Code.
Modify the code to include the following:

x = 5
y = 10

if x < y:
    print("x is less than y")

This code checks if x is less than y. If it is, it prints the message "x is less than y".

Save the changes and run the script again:

python ~/project/conditions.py

You should see the following output:

x is less than y

This output shows that the code inside the if statement was executed because the condition x < y was true.

You can also add an else clause to an if statement. The else clause allows you to execute a different block of code if the condition is false.

The syntax of an if-else statement is:

if condition:
    ## Code to execute if the condition is true
else:
    ## Code to execute if the condition is false

Let's modify the conditions.py script to include an else clause.

Open the conditions.py file in VS Code.
Modify the code to include the following:

x = 15
y = 10

if x < y:
    print("x is less than y")
else:
    print("x is greater than or equal to y")

This code checks if x is less than y. If it is, it prints the message "x is less than y". Otherwise, it prints the message "x is greater than or equal to y".

Save the changes and run the script again:

python ~/project/conditions.py

You should see the following output:

x is greater than or equal to y

This output shows that the code inside the else clause was executed because the condition x < y was false.

Finally, you can add an elif (else if) clause to an if statement. The elif clause allows you to check multiple conditions in a sequence.

The syntax of an if-elif-else statement is:

if condition1:
    ## Code to execute if condition1 is true
elif condition2:
    ## Code to execute if condition1 is false and condition2 is true
else:
    ## Code to execute if both condition1 and condition2 are false

Let's modify the conditions.py script to include an elif clause.

Open the conditions.py file in VS Code.
Modify the code to include the following:

x = 10
y = 10

if x < y:
    print("x is less than y")
elif x > y:
    print("x is greater than y")
else:
    print("x is equal to y")

This code checks if x is less than y. If it is, it prints the message "x is less than y". If x is greater than y, it prints the message "x is greater than y". Otherwise, it prints the message "x is equal to y".

Save the changes and run the script again:

python ~/project/conditions.py

You should see the following output:

x is equal to y

This output shows that the code inside the else clause was executed because both conditions x < y and x > y were false.

if statements are essential for creating programs that can make decisions and respond to different situations. In the next step, you will learn how to use the and and or operators to combine multiple conditions in your if statements.

Use and/or Operators to Combine Conditions

In this step, you will learn how to use the and and or operators to combine multiple conditions in Python if statements. These operators allow you to create more complex and flexible decision-making logic in your programs.

The and operator returns True if both conditions on either side of the operator are True. Otherwise, it returns False.

The or operator returns True if at least one of the conditions on either side of the operator is True. It returns False only if both conditions are False.

Let's start by exploring the and operator. You will modify the conditions.py script you created in the previous steps.

Open the conditions.py file in VS Code.
Modify the code to include the following:

x = 5
y = 10
z = 15

if x < y and y < z:
    print("x is less than y and y is less than z")

This code checks if x is less than y and y is less than z. If both conditions are true, it prints the message "x is less than y and y is less than z".

Save the changes and run the script again:

python ~/project/conditions.py

You should see the following output:

x is less than y and y is less than z

This output shows that the code inside the if statement was executed because both conditions x < y and y < z were true.

Now, let's explore the or operator.

Open the conditions.py file in VS Code.
Modify the code to include the following:

x = 15
y = 10
z = 5

if x < y or y < z:
    print("x is less than y or y is less than z")

This code checks if x is less than y or y is less than z. If at least one of the conditions is true, it prints the message "x is less than y or y is less than z".

Save the changes and run the script again:

python ~/project/conditions.py

You should see the following output:

x is less than y or y is less than z

This output shows that the code inside the if statement was executed because the condition y < z was true (even though x < y was false).

You can also combine the and and or operators in the same if statement. When doing so, it's important to use parentheses to specify the order of operations.

Open the conditions.py file in VS Code.
Modify the code to include the following:

x = 5
y = 10
z = 15
w = 20

if (x < y and y < z) or w < z:
    print("(x < y and y < z) or w < z")

This code checks if (x < y and y < z) is true or w < z is true. The parentheses ensure that the and operation is performed before the or operation.

Save the changes and run the script again:

python ~/project/conditions.py

You should see the following output:

(x < y and y < z) or w < z

This output shows that the code inside the if statement was executed because the condition (x < y and y < z) was true.

By using the and and or operators, you can create more sophisticated and powerful decision-making logic in your Python programs. This allows you to handle a wider range of scenarios and create more flexible and adaptable code.

Summary

In this lab, you learned about Boolean conditions in Python, which are expressions that evaluate to either True or False. You explored the basic Boolean values (True and False) and common comparison operators such as ==, !=, >, <, >=, and <=. You practiced using these operators in a Python script to compare variables and print the resulting Boolean values.

Furthermore, the lab introduced Boolean operators like and, or, and not for combining multiple conditions, although the full explanation of these operators was truncated.