Python - If-Else Statements

If Statement

The If statement is used to execute a block of code when the condition is evaluated to be true. When the condition is evaluated to be false, the program will skip the if-code block.

Syntax

if condition:
  statements

Flow Diagram:

In the example below, a if code block is created which executes only when the variable i is divisible by 3.

i = 15
if i % 3 == 0:
  print(i," is divisible by 3.")

The output of the above code will be:

15 is divisible by 3.

If-else Statement

The else statement is always used with if statement. It is used to execute block of codes whenever if condition gives false result.

Syntax

if condition:
  statements
else:
  statements

Flow Diagram:

In the example below, else statement is used to print a message if the variable i is not divisible by 3.

i = 16
if i % 3 == 0:
  print(i," is divisible by 3.")
else:
  print(i," is not divisible by 3.")

The output of the above code will be:

16 is not divisible by 3.

elif Statement

For adding more conditions, elif statement in used. The program first checks if condition. When found false, it checks elif conditions. If all elif conditions are found false, then else code block is executed.

Syntax

if condition:
  statements
elif condition:
  statements
...
...
...
else:
  statements

Flow Diagram:

In the example below, elif statement is used to add more conditions between if statement and else statement.

i = 16
if  i > 25:
  print(i," is greater than 25.") 
elif i <=25 and i >=10:
  print(i," lies between 10 and 25.") 
else:
  print(i," is less than 10.")

The output of the above code will be:

16 lies between 10 and 25.

Short hand if

When if has only one statement to execute, the code can be written in a single line as described in the example below.

i = 15
if  i % 3 == 0 : print(i," is divisible by 3.") 

The output of the above code will be:

15  is divisible by 3.

Short hand if-else

When if and else both have only one statement to execute, the code can be written in a single line as described in the example below.

i = 16
print(i," is divisible by 3.") \
  if  i % 3 == 0 else print(i," is not divisible by 3.")  

The output of the above code will be:

16  is not divisible by 3.