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

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())

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

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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