In this post, we will write a program for how to calculate the area of a circle in python.
First, let’s see What is the Area of Circle?
The area enclosed by a circle of radius r in 2-dimensional plane.
Formula:

Area of circle: A = pi * r * r Or pi * r 2
Where,
r = Radius of circle 
pi = pi is geek letter which is a constant whose approximate value is 3.14159...

Examples:

Input: Radius = 7
Output: The area of the circle is 154.0

Input: Radius = 2
Output: The area of the circle is 12.56

Let’s see the program for this:
Code Version 1: Create a user-defined function that will calculate and print the area of a circle.

# define a function for
# finding area of a circle 
def area(r):
        
        # constant value of PI
	PI = 22/7
	
	# printing the radius
	print("Radius =", r)
	
	# calculating the area
	area = PI * (r * r)
	
	# printing the area
	print("The area of the circle is", area)

# main code
if __name__ == "__main__" :

    # input radius
    radius = 7

    # function calling
    area(radius)	

Output:

Radius = 7
The area of the circle is 154.0

Code Version 2: Create a user-defined function that will calculate and print the area of a circle. In this code version, we are using pi constant value which is directly taken from the math library.

# including pi constant
# from the math library
# into this program
from math import pi

# defina a function for
# finding area of circle 
def area(r):

	
	# printing the radius
	print("Radius =", r)
	
	# calculating the area
	area =  pi * (r * r)
	
	# printing the area
	print("The area of the circle is", area)

# main code
if __name__ == "__main__" :

    # input radius
    radius = 7

    # function calling
    area(radius)

Output:

Radius = 7
The area of the circle is 153.93804002589985