Python if...else Statement

In computer programming, the if statement is a conditional statement. It is used to execute a block of code only when a specific condition is met. For example,

Suppose we need to assign different grades to students based on their scores.

1. If a student scores above 90, assign grade A
2. If a student scores above 75, assign grade B
3. If a student scores above 65, assign grade C

These conditional tasks can be achieved using the if statement.

Python if Statement

An if statement executes a block of code only if the specified condition is met.

Syntax

if condition:
    # body of if statement

Here, if the condition of the if statement is:

• True - the body of the if statement executes.
• False - the body of the if statement is skipped from execution.

Let's look at an example.

if number > 0:
    print('Number is positive')

Example: Python if Statement

number = 10

# check if number is greater than 0
if number > 0:
    print('Number is positive')

print('This statement always executes')

Sample Output 1

Number is positive
This statement always executes

In the above example, we have created a variable named number. Notice the test condition,

number > 0 

As the number is greater than 0, the condition evaluates True. Hence, the body of the if statement executes.

Sample Output 2

Now, let's change the value of the number to a negative integer, say -5.

number = -5

Now, when we run the program, the output will be:

This statement always executes

This is because the value of the number is less than 0. Hence, the condition evaluates to False. And, the body of the if statement is skipped.

Python if...else Statement

An if statement can have an optional else clause. The else statement executes if the condition in the if statement evaluates to False.

Syntax

if condition:
    # body of if statement

else:
    # body of else statement

Here, if the condition inside the if statement evaluates to

• True - the body of if executes, and the body of else is skipped.
• False - the body of else executes, and the body of if is skipped

Let's look at an example.

Example: Python if…else Statement

number = 10

if number > 0:
    print('Positive number')

else:
    print('Negative number')

print('This statement always executes')

Sample Output 1

Positive number
This statement always executes

In the above example, we have created a variable named number.

Since the value of the number is 10, the condition evaluates to True. Hence, code inside the body of if is executed.

Sample Output 2

If we change the value of the variable to a negative integer, let's say -5, our output will be:

Negative number
This statement always executes

Here, the test condition evaluates to False. Hence code inside the body of else is executed.

Python if…elif…else Statement

The if...else statement is used to execute a block of code among two alternatives.

However, if we need to make a choice between more than two alternatives, we use the if...elif...else statement.

Syntax

if condition1:
    # code block 1

elif condition2:
    # code block 2

else: 
    # code block 3

Here,

• if condition1 - This checks if condition1 is True. If it is, the program executes code block 1.

• elif condition2 - If condition1 is not True, the program checks condition2. If condition2 is True, it executes code block 2.

• else - If neither condition1 nor condition2 is True, the program defaults to executing code block 3.

Let's look at an example.

Example: Python if…elif…else Statement

number = 0

if number > 0:
    print('Positive number')

elif number <0:
    print('Negative number')

else:
    print('Zero')

print('This statement is always executed')

Output

Zero
This statement is always executed

In the above example, we have created a variable named number.

Since the value of the number is 0, both the test conditions evaluate to False.

Hence, the statement inside the body of else is executed.

Python Nested if Statements

It is possible to include an if statement inside another if statement. For example,

number = 5

# outer if statement
if number >= 0:
    # inner if statement
    if number == 0:
      print('Number is 0')
    
    # inner else statement
    else:
        print('Number is positive')

# outer else statement
else:
    print('Number is negative')

Output

Number is positive

Here's how this program works.

number = 10

if number > 0:
    print('Positive')

number = 10

if number>0: print('Positive')

grade = 40

if grade >= 50:
    result = 'pass'
else:
    result = 'fail'

print(result)

grade = 40

result = 'pass' if number >= 50 else 'fail'

print(result)

age = 35
salary = 6000

# add two conditions using and operator
if age >= 30 and salary >= 5000:
    print('Eligible for the premium membership.')
else:
    print('Not eligible for the premium membership')

Eligible for the premium membership.

Also Read

• Python pass Statement
• Python break and continue