In this post, we will write a program for how to calculate circumference of a circle in python.
First, let’s see What is Circumference of Circle?
The perimeter is the curve length around any closed figure.
Formula:

Circumference of Circle: C = 2 * pi * r
Where,
r = Radius of circle 
pi = pi is geek letter which is a constant whose approximate value is 3.14159.. or 22/7 .

Examples:

Input: Radius = 5
Output: The circumference of the circle is 31.40.

Input: Radius = 2
Output: The circumference 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 circumference of a circle.

# define a function for
# calculating circumference
# of a circle
def circumference_circle(r):

        # constant value
	PI = 3.14
	
	# printing the radius
	print("Radius =",r)
	
	# calculating the circumference
	C = 2 * PI * r
	
	# printing the circumference
	print("The circumference of the circle is",
              C)

# main code
if __name__ == "__main__" :

   # input radius
    radius = 5
 
    # function calling
    circumference_circle(radius)

Output:

Radius = 5
The circumference of the circle is 31.400000000000002

Code Version 2: Create a user-defined function that will calculate and print the circumference 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

# define a function for
# calculating circumference
# of a circle
def circumference_circle(r):
	
	# printing the radius
	print("Radius =",r)
	
	# calculating the circumference
	C = 2 * pi * r
	
	# printing the circumference
	print("The circumference of the circle is",
              C)

# main code
if __name__ == "__main__" :

   # input radius
    radius = 2
 
    # function calling
    circumference_circle(radius)	

Output:

Radius = 2
The circumference of the circle is 12.566370614359172

Code version 3: Create a user-defined one-line anonymous function which will calculate and return the circumference of a circle using a lambda statement.

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

# main code
if __name__ == "__main__" :

    # input radius
    radius = 2

    # printing the radius
    print("Radius =", radius)

    # create a one line function
    # using lambda statement
    # for calculating
    # circumference of a
    # circle
    circumference_circle = lambda r : 2 * pi * r

    # function calling
    print("The circumference of the circle is",
          circumference_circle(radius))

Output:

Radius = 2
The circumference of the circle is 12.566370614359172