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      If-else Statement

      Python Tutorial

      This Python tutorial has been written for the beginners to help them understand the basic to advanced concepts of Python Programming Language. After completing this tutorial, you will find yourself at a great level of expertise in Python, from where you can take yourself to the next levels to become a world class Software Engineer.

      If-else Statement

      Python − if-else Statement

      Along with the if statement, else keyword can also be optionally used. It provides an alternate block of statements to be executed if the Boolean expression (in if statement) is not true. this flowchart shows how else block is used.
      
      If the expr is True, block of stmt1,2,3 is executed then the default flow continues with stmt7. However, the If expr is False, block stmt4,5,6 runs then the default flow continues.

      Syntax

      Python implementation of the above flowchart is as follows 
      if expr==True:
         stmt1
         stmt2
         stmt3
      else:
         stmt4
         stmt5
         stmt6
      Stmt7

      Example

      Let us understand the use of else clause with following example. The variable age can take different values. If the expression "age > 18" is true, message you are eligible to vote is displayed otherwise not eligible message should be displayed. Following flowchart illustrates this logic.
      
      Its Python implementation is simple.
      age=25
      print ("age: ", age)
      if age >=18:
         print ("eligible to vote")
      else:
         print ("not eligible to vote")
      To begin, set the integer variable "age" to 25.
      Then use the if statement with "age>18" expression followed by ":" which starts a block; this will come in action if "age>=18" is true.
      To provide else  block, use else: the ensuing indented block containing message not eligible will be in action when "age>=18" is false.
      On executing this code, you will get the following ouput
      age: 25
      eligible to vote
      To test the the else block, change the age to 12, and run the code again.
      age: 12
      not eligible to vote

      Python − elif Statement

      The elif 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 the else statement, the elif statement is optional. However, unlike else, for which there can be at the most one statement; there can be an arbitrary number of elif statements following an if.

      Syntax

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

      Example

      Let us understand how elif works, with the help of following example.
      The discount structure used in an earlier example is modified to different slabs of discount
      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
      

      Example

      We can write a Python code for the above logic with if-else statements
      amount = 2500
      print('Amount = ',amount)
      if amount > 10000:
         discount = amount * 20 / 100
      else:
         if amount > 5000:
            discount = amount * 10 / 100
         else:
            if amount > 1000:
               discount = amount * 5 / 100
            else:
               discount = 0
      
      print('Payable amount = ',amount - discount)
      Set amount to test all possible conditions: 800, 2500, 7500 and 15000. The outputs will vary accordingly
      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 ok, 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.
      The elif statement makes the code easy to read and comprehend.
      Elif is short for else if. It allows the logic to be arranged in a cascade of elif statements after the first if statement. If the first if statement evaluates to false, subsequent elif statements are evaluated one by one and comes out of the cascade if any one is satisfied.
      Last in the cascade is the else block which will come in picture when all preceding if/elif conditions fail.
      amount = 2500
      print('Amount = ',amount)
      if amount > 10000:
         discount = amount * 20 / 100
      elif amount > 5000:
         discount = amount * 10 / 100
      elif amount > 1000:
         discount = amount * 5 / 100
      else:
         discount=0
      
      print('Payable amount = ',amount - discount)
      Set amount to test all possible conditions: 800, 2500, 7500 and 15000. The outputs will vary accordingly
      Amount: 800
      Payable amount = 800
      Amount: 2500
      Payable amount = 2375.0
      Amount: 7500
      Payable amount = 6750.0
      Amount: 15000
      Payable amount = 12000.0

      Practice with Online Editor

      Note: This Python online Editor is a Python interpreter written in Rust, RustPython may not fully support all Python standard libraries and third-party libraries yet.
      Remember to save code(Ctrl + S Or Command + S) before run it.