Python If – Syntax & Example

IF statement in Python

The Python If statement is a conditional statement where a set of statements executes based on the result of a condition.

In this Python example, we will learn about the Python If statement syntax and the different situations in which Python If command can be used.

Following is the flow diagram of the if statement in Python. Based on the evaluation of the condition, the program execution takes one of the paths.

Python If . Syntax

Following is the syntax of the if statement in Python.

if boolean_expression:
    statement(s)

Observe the indent provided for the statement(s) inside the if block and the colon : after the boolean expression.

If the boolean expression returns true, the if block’s statement(s) will be executed. Otherwise, the statement(s) is not executed and program execution continues with statements after the if statement, if any.

The following is a diagram that describes the execution of the condition and the statements in the if statement.

 

Example 1: PythonIf

In this example, we will use a simple boolean expression created with the relational operator, less than, for the if statement condition. The statement(s) inside the if block is just a single print statement.

Python Program

a = 2
b = 5

if a<b:
	print(a, 'is less than', b)

 

Output

Run the program and you will see the following output in the console.

2 is less than 5

It is important that the condition provided in the if statement above evaluates to true, so the statement(s) inside the if block are executed.

 

Example 2: Python If Statement where Boolean Expression is False

In this example, we will write a if statement in which a boolean expression or condition evaluates to false.

Python Program

a = 24
b = 5

if a<b:
	print(a, 'is less than', b)

 

Output

The condition provided in the if statement evaluates to false, and therefore the statement inside the if block is not executed.

 

Example 3: Python If with Multiple Conditions in the Expression

When you need to write multiple conditions in a single expression, use logical operators to join them and create a compound condition. The logical operators could be: python and, python or or python not.

Python Program

a = 2
b = 5
c = 4

if a<b and a<c:
	print(a, 'is less than', b, 'and', c)

Output

a<b is true and a<c that right. As a result, all conditions are true.

2 is less than 5 and 4

 

Example 4: Python If with Expression evaluates to a number

If the expression in the if statement evaluates to a number, then the statement(s) is executed if the number is non-zero 0. 0 is considered false and non-zero (positive or negative) is considered true.

In this example, we’ll write a Python If statement, where the boolean expression evaluates to a number.

Python Program

a = 2

if a:
	print(a, 'is not zero')

Output

Since the value of the evaluated condition is 2is a non-zero number, the statement(s) inside the if block are executed.

2 is not zero.

 

Example 5: Python If with multiple statements in a block

In the syntax section, we mentioned that there can be multiple statements inside if block.

In this example we will write three statements inside if block.

Python Program

a = 2

if a:
	print(a, 'is not zero')
	print('And this is another statement')
	print('Yet another statement')

We just write the print statements in this example inside the if block. But you can write a set of any valid python statement(s) inside the if block.

Please note that if-block statements have the same indented in.

Output

2 is not zero
And this is another statement
Yet another statement

 

Example 6: If nested

You can write a Python If statement inside another Python If statement. This is called nesting.

In this example, we will write a nested if block: an if block inside another if block.

Python Program

a = 2

if a!=0:
	print(a, 'is not zero.')
	if a>0:
		print(a, 'is positive.')
	if a<0:
		print(a, 'is negative.')

Output

As the first/external condition a!=0 evaluates to true, execution goes into the if block. And the if statements inside this outer if block are treated as another Python statement and executed accordingly.

2 is not zero.
2 is positive.

 

Summary

In this guide of Python example we have learned what is If statement in Python, what is it used for, how to write nested if, if statements, all with the help of some detailed examples.