Python if statement runs either one set of statements or another set of statements depending upon the condition associated with. If, if-else, and if elif are three selection statements available in Python.

Before anything else, let’s clear the concept of  single statement and compound statement

Single Statement: Any valid Python statement.
Compound Statement: Group of statement that executes as a single statement.

If Statement

It will execute its associated statement only once its associated condition results in True. If associated condition is not True then it will skip the associated statement and will move on next statement.

Syntax

if condition:
     statement

if statement is the first selection statement that checks the associated condition with. Runs the associated statement(s), if the result is true otherwise control jumps on the very next statement.

Flow Diagram of if statement

Example of if statement

age =18 
if age < 20:
   print(' You are minor my dear'

The output of the above code is

 You are minor my dear

if-else statement

If statement is a selection statement i.e. it will execute its associated statement only once its associated condition results in True. If the associated condition is not True then it will skip the associated statement and will move on to the statement associated with ELSE.

Syntax

if condition:
      statement-1
else:
     statement-2

Flow Diagram of if-else statement

Sample program to demonstrate the working of if-else statement

age =21
if age >20 :
   print(' You are minor my dear')
else:
  print(' You are major my dear.... Welcome to the club')

The sample output of the above program is

    You are major my dear.... Welcome to the club

if you have multiple such conditions then how to deal with that condition. Let’s consider a situation where you are given a day number and you are requested to generate its associated day name.

probable solution using only if statement

dno =int(input(“Enter day Number”))
If(dno==1):
   print(“Monday”)
If(dno==2):
   print(“Tuesday”)
If(dno==3):
   print(“Wednesday”)
If(dno==4):
   print(“Thursday”)
If(dno==5):
   print(“Fridday”)
If(dno==6):
   print(“Saturday”)
If(dno==7):
   print(“Sundayday”)

using if elif statement – Compare multiple conditions

dno =int(input(“Enter day Number”))
If(dno==1):
   print(“Monday”)
   elif(dno==2):
        print(“Tuesday”)
        elif(dno==3):
             print(“Wednesday”)
             elif(dno==4):
                  print(“Thursday”)
                  elif(dno==5):
                      print(“Fridday”)
                      elif(dno==6):
                          print(“Saturday”)
                          elif(dno==7):
                               print(“Sundayday”)

The last one is a better solution as it compares fewer numbers compared to the previous solution. Indentation is one of the most important parts of the selection statement. The improperly indented statement will raise logical errors.  unlike other programming languages, Python does not support a switch statement.

Python Assignment on if  statement is one such article that you must try with this if statement tutorial.