February 11, 2018

Python program to calculate circle area

Introduction

Welcome to a new code snippet in Python. This post is a beginner level one in which we are going to implement a basic Python class to represent a circle and be able to compute the area using different methods. You will learn how to define a class in Python, use default parameter values and utilize the math module. Let us do that…

Circle area

Circle area can be calculated in difference ways…

Area = PI * R * R where R is the radius
Area = (PI * D * D)/4 where D is the diameter
Area = (C * C/4 * PI) where C is the circumference

Area = PI * R * R where R is the radius

Area = (PI * D * D)/4 where D is the diameter

Area = (C * C/4 * PI) where C is the circumference

Let us implement these formulas in Python…

Circle area in Python

# Import math module so that we can use pi
import math

# Define a circle class
class Circle:
    # Constructor: initialize with 
    # radius or diameter or circumference
    # For example, if you do not want to
    # use the radius, just leave it 0
    # Note that we used default values of 0
    # It is a trick to know how the user
    # wants to calculate the area
    def __init__(self, r=0, d=0, c=0):   
        # Radius
        self.r = r
        # Diameter
        self.d = d 
        # Circumference
        self.c = c

    # Calculate area
    def area(self):
        # Using radius
        if self.r > 0:
            # ** is used to raise a number to a power
            return math.pi * self.r ** 2
        # Using diameter
        if self.d > 0:
            return (math.pi * self.d ** 2)/4
        # Using circumference
        if self.c > 0:
            return (self.c ** 2)/(4 * math.pi)

# Create a circle object to test our code

# Using radius, note that we did not provide
# values for diameter and circumference so
# the default values are going to be 0 therefore
# they are not going to be used in the calculation
circle = Circle(10)
print(circle.area())

# Using diameter, note that the first parameter
# has to be provided even though we do not want
# to use it in the calculation
circle = Circle(0, 10)
print(circle.area())

# Using circumference, note that the first and second
# parameters need to be provided even though they are
# not used in the calculation
circle = Circle(0, 0, 10)
print(circle.area())

# Import math module so that we can use pi

import math

# Define a circle class

class Circle:

# Constructor: initialize with

# radius or diameter or circumference

# For example, if you do not want to

# use the radius, just leave it 0

# Note that we used default values of 0

# It is a trick to know how the user

# wants to calculate the area

def __init__(self, r=0, d=0, c=0):

# Radius

self.r = r

# Diameter

self.d = d

# Circumference

self.c = c

# Calculate area

def area(self):

# Using radius

if self.r > 0:

# ** is used to raise a number to a power

return math.pi * self.r ** 2

# Using diameter

if self.d > 0:

return (math.pi * self.d ** 2)/4

# Using circumference

if self.c > 0:

return (self.c ** 2)/(4 * math.pi)

# Create a circle object to test our code

# Using radius, note that we did not provide

# values for diameter and circumference so

# the default values are going to be 0 therefore

# they are not going to be used in the calculation

circle = Circle(10)

print(circle.area())

# Using diameter, note that the first parameter

# has to be provided even though we do not want

# to use it in the calculation

circle = Circle(0, 10)

print(circle.area())

# Using circumference, note that the first and second

# parameters need to be provided even though they are

# not used in the calculation

circle = Circle(0, 0, 10)

print(circle.area())

If you run the code snippet above, you should get the following output…

314.159265359
78.5398163397
7.95774715459

314.159265359

78.5398163397

7.95774715459

Summary

Circle area can be calculated in different ways depending on what we know in advance such as the radius, diameter or circumference
Class keyword in Python is used to define a class of objects. To provide a constructor, use __init__ method
We can provide default values to method parameters in method signature
Math module is a good choice for all sorts of mathematical computation. In this post, we used math.pi

Thanks for reading. Please use the comments section below for feedback.

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Python program to calculate circle area

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