PYTHON - If else

Python if-else Statement

Python if else Statement

The if-else statement inPythonis used to execute a block of code when the condition in theif statementis 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 −

PYTHON CODE

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

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

Flowchart of if-else Statement

This flowchart shows how if-else statement is used −

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

Python implementation of the above flowchart is as follows −

PYTHON CODE

if expr==True:
   stmt1
   stmt2
   stmt3
else:
   stmt4
   stmt5
   stmt6
Stmt7

Python if-else Statement Example

Let us understand the use ofif-elsestatements with the following example. Here, variableagecan take different values. If the expressionage > 18is true, theneligible to votemessage will be displayed otherwisenot eligible to votemessage will be displayed. Following flowchart illustrates this logic −

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

PYTHON CODE

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

On executing this code, you will get the followingoutput−

PYTHON CODE

age: 25
eligible to vote

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

PYTHON CODE

age: 12
not eligible to vote

Python if elif else Statement

Theif elif elsestatement 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 blockis also optional. However, a program can contains only oneelse blockwhereas there can be an arbitrary number ofelif blocksfollowing anif block.

Syntax of Python if elif else Statement

PYTHON CODE

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

How if elif else Works?

The keywordelifis a short form ofelse if. It allows the logic to be arranged in a cascade ofelifstatements after the firstifstatement. If the firstifstatement evaluates to false, subsequentelifstatements are evaluated one by one and comes out of the cascade if any one is satisfied.

Last in the cascade is theelseblock 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-elsestatements −

PYTHON CODE

amount = 2500
print('Amount = ',amount)
if amount &gt; 10000:
   discount = amount * 20 / 100
else:
   if amount &gt; 5000:
      discount = amount * 10 / 100
   else:
      if amount &gt; 1000:
         discount = amount * 5 / 100
      else:
         discount = 0

print('Payable amount = ',amount - discount)

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

PYTHON CODE

Amount: 800
Payable amount = 800
Amount: 2500
Payable amount = 2375.0
Amount: 7500
Payable amount = 6750.0
Amount: 15000
Payable 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 statementmakes the code easy to read and comprehend. Following is the Python code for the same logic with if elif else statements −

PYTHON CODE

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

print('Payable amount = ',amount - discount)

The output of the above code is as follows −

PYTHON CODE

Amount: 2500
Payable amount = 2375.0