if, if else, if elif else and nested if else in Python. 

In this post we are going to learn about if , if else , if elif else and nested if else in Python. Let's start..!

This if else is used for checking conditions in Python. This statement ( if else ) decides a flow of program. It simply means depend upon condition next statements will execute. 

Syntax : if condition : 

                    if block statements

               else : 

                    else block statements

Here if the condition is true then if block statements will executes. Else the else block statements will executes. 

for ex. Suppose

We have a variable a = 5 and we want print message that a is greater than 10 or less than 10. To achieve this we will check a condition using if else conditional statements and we will print result that a is greater than 10 or less than 10. 

# using if else conditional statements

a = 5

if a > 10:

    print("\n a is greater than 10 ")

else:

    print("\n a is less than 10 ")

Here a is 5 so a is not greater than 10 and our condition is false so else block will execute and will print a is less than 10. 

Here I am giving some spaces before a print statements What is that ? and Why I give spaces there ? 

Indentation :

This is Indentation in Python. It simply means you don't need to give curly brackets ( { } ) there to define a block. Block means a bunch of statements or code . To define block in Python you have to give a exact four spaces ( only 4 spaces ; more than 4 or less than 4 spaces not allowed; otherwise this will raise an error ) according to the start of previous line and write all statements in same line as first statement in block You will learn this things better in further posts and programs . 

Here if our condition is true then if block will execute, Else else block will execute. But when your given condition is false and still want to apply some conditions and then based on that condition print the result. For this we have a special elif statement .

Syntax : if condition : 

                    if block of first condition 

               elif condition :

                     if block of second condition

                else:

                      common else block 

Here if the first condition is true then if block statements will executes. Else it will check second condition or elif condition and if second condition is true then second if block statements will executes. Else last else block statements will executes. 

For ex. Suppose

We have a variable a = 15 and we want print message that a is greater than 20 or less than 20; and if the a is less than 20 then we want to check again that a is greater than 10 or less than 10. To achieve this we will first check a condition to know a is greater than 20 or less than 20  and if a is less than 20 then we will check a condition to know a is greater than 10 or less than 10 Now based on this we will print result.

# using if elif else conditional statements

a = 15

if a > 20:

    print("\n a is greater than 20 ")

elif a > 10:

    print("\n a is less than 20 but a is grater than 10 ")

else:

    print("\n a is less than 20 and less than 10 also ")

Here a is 15 so a is not greater than 20 and our condition is false so check for second condition;  here a = 15 so a is greater than 10 now we will print a is less than 20 but a is greater than 10. 

Now learn about Nested if else What is this ?  This is very simple concept. Simply writing if  else statements inside a if block or a else block. 

Syntax : 

               if condition : 

                    if condition: 

                            inner if block

                    outer if block

               else : 

                    else block statements

Here if the first condition is true then if block statements will executes with this inner if condition is true then inner if block will executes. Else  else block statements will executes. 

for ex. Suppose 

We have a variable a = 10 want to check a is greater than 5 or less than 5 and if a is greater than 5 then check for a is equal to 5 or not and print result accordingly. 

# using nested if else conditional statements

a = 10

if a > 5:

    print("\n a is greater than 5 ")

    # nested if else

    if a == 5:

        print(" a is equal to 5 ")

    else:

        print(" a is not equal to 5 ")

else:

    print("\n a is less than 20 and less than 10 also ")

Here a is 10 so a is greater than 5 so our condition is true so check for second condition; here a = 10 so a is not equal to 5 now we will print a is greater than 5 a is not equal to 5. 

Sometimes we want to print a message only if the condition is true and don't want print anything if condition is false. In this case we can use only if statement. Simply write a if statement and if block .

Syntax : 

if condition :

    if block statements  

Here if the condition is true then if block statements will executes. Otherwise this will skip if block and continues the execution.  

for ex. Suppose

We have a variable a = 10 and we want to check a is equal to 5. we want print a result only if condition is true else don't show anything.

# using if conditional statement

a = 10

if a == 5:

   print(" a is equal to 5 ")

  

Here a = 10 and a is not equal to 5 so this will not print anything.

This is all about if , if else , if elif else and nested if else conditional statements in Python. Try this all conditional statements for checking various conditions.

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