Python if-else Statement

Python if else Statement

The if-else statement inPython is used to execute a block of code when the condition in theif statement is true, and another block of code when the condition is false.

Syntax of if-else Statement

The syntax of an if-else statement in Python is as follows −

if boolean_expression:  # code block to be executed  # when boolean_expression is trueelse:  # code block to be executed  # when boolean_expression is false

If the boolean expression evaluates to TRUE, then the statement(s) inside theif block will be executed otherwise statements of theelse block will be executed.

Flowchart of if-else Statement

This flowchart shows how if-else statement is used −

If theexpr is True, block of stmt1, 2, 3 is executed then the default flow continues with stmt7. However, if theexpr is False, block stmt4, 5, 6 runs then the default flow continues.

Python implementation of the above flowchart is as follows −

if expr==True:   stmt1   stmt2   stmt3else:   stmt4   stmt5   stmt6Stmt7

Python if-else Statement Example

Let us understand the use ofif-else statements with the following example. Here, variableage can take different values. If the expressionage > 18 is true, theneligible to vote message will be displayed otherwisenot eligible to vote message will be displayed. Following flowchart illustrates this logic −

Now, let's see the Python implementation the above flowchart.

age=25print ("age: ", age)if age >=18:   print ("eligible to vote")else:   print ("not eligible to vote")

On executing this code, you will get the followingoutput −

age: 25eligible to vote

To test theelse block, change theage to 12, and run the code again.

age: 12not eligible to vote

Python if elif else Statement

Theif elif else statement allows you to check multiple expressions for TRUE and execute a block of code as soon as one of the conditions evaluates to TRUE.

Similar to theelse block, theelif block is also optional. However, a program can contains only oneelse block whereas there can be an arbitrary number ofelif blocks following anif block.

Syntax of Python if elif else Statement

if expression1:   statement(s)elif expression2:   statement(s)elif expression3:   statement(s)else:   statement(s)

How if elif else Works?

The keywordelif is a short form ofelse if. It allows the logic to be arranged in a cascade ofelif statements after the firstif statement. If the firstif statement evaluates to false, subsequentelif statements are evaluated one by one and comes out of the cascade if any one is satisfied.

Last in the cascade is theelse block which will come in picture when all preceding if/elif conditions fails.

Example

Suppose there are different slabs of discount on a purchase −

• 20% on amount exceeding 10000,

• 10% for amount between 5-10000,

• 5% if it is between 1 to 5000.

• no discount if amount<1000

The following flowchart illustrates these conditions −

We can write a Python code for the above logic withif-else statements −

amount = 2500print('Amount = ',amount)if amount > 10000:   discount = amount * 20 / 100else:   if amount > 5000:      discount = amount * 10 / 100   else:      if amount > 1000:         discount = amount * 5 / 100      else:         discount = 0print('Payable amount = ',amount - discount)

Setamount to test all possible conditions: 800, 2500, 7500 and 15000. The outputs will vary accordingly −

Amount: 800Payable amount = 800Amount: 2500Payable amount = 2375.0Amount: 7500Payable amount = 6750.0Amount: 15000Payable amount = 12000.0

While the code will work perfectly fine, if you look at the increasing level of indentation at each if and else statement, it will become difficult to manage if there are still more conditions.

Python if elif else Statement Example

Theelif statement makes the code easy to read and comprehend. Following is the Python code for the same logic with if elif else statements −

amount = 2500print('Amount = ',amount)if amount > 10000:   discount = amount * 20 / 100elif amount > 5000:   discount = amount * 10 / 100elif amount > 1000:   discount = amount * 5 / 100else:   discount=0print('Payable amount = ',amount - discount)

The output of the above code is as follows −

Amount: 2500Payable amount = 2375.0