# Using Python to try to use object-oriented design method to calculate the area and perimeter of graphics

Using Python to try to adopt the object-oriented design method.
(1) design a base class Shape:
There are two member functions:
def cal_area(): calculate and return the area of the figure, with two decimal places reserved;
def cal_perimeter(): calculates and returns the perimeter of the graph, retaining two decimal places.
def display(): three lines of string, showing name, area and perimeter respectively, rounding the value and keeping two
Decimal places, as follows:
The name is rect
The area is 6.
The circumference is 10.
There are three variables:
Name: indicates the name, string type;
Area: area, number;
Perimeter: perimeter, number.
(2) three derived classes are designed: Rectangle, Triangle and Circle. The derived classes implement two of the base classes respectively
Operator function.
Rectangle: constructor parameter (n, a, b), n is the name, others are floating-point numbers, two decimal places, a, B points
Don't represent length and width.
Triangle: constructor parameter (n, a, b, c), n is the name, others are floating-point numbers, two decimal places, representing three
The length of the edge.
Circle: constructor parameter (n, a), n is name, a is floating point number, two decimal places, representing radius of circle, circle
The weekly rate is calculated as 3.14.

```#!/usr/bin/python
# -*- coding: UTF-8 -*-
#Topic 8: calculate the area and perimeter of the figure
import math
class Shape:

def __init__(self,name,area,perimeter):
self.name = name
self.area = area
self.perimeter = perimeter
def cal_area(self):
pass
def cal_perimeter(self):
pass
def display(self):
print('Name:',self.name)
print('The measure of area:',self.area)
print('Perimeter:',self.perimeter)
class Rectangle(Shape):
def __init__(self,n,a,b):
self.n = n
self.a=a
self.b=b
def cal_area(self):
area = round (self.a * self.b, 2)
def cal_perimeter(self,):
perimeter=round(2*(self.a+self.b),2)

class Triangle(Shape):
def __init__(self,n,a,b,c):
self.n=n
self.a=a
self.b=b
self.c=c
def cal_area(self):
p=(self.a+self.b+self.c)/2
area=round(math.sqrt(p*(p-self.a)*(p-self.b)*(p-self.c)),2)
return area

def cal_perimeter(self):
perimeter=self.a+self.b+self.c
return perimeter

class Circle(Shape):
def __init__(self,n,a):
self.n = n
self.a=a
def cal_perimeter(self):
perimeter=round(2*3.14*self.a,2)
return perimeter
def cal_area(self):
area=round(3.14*self.a**2,2)
return area

if __name__ == '__main__':
cir=Circle('cir',3)
result=Shape(cir.n,cir.cal_area(),cir.cal_perimeter())
result.display()

ret=Rectangle('ret',4,5)
result=Shape(ret.n,ret.cal_area(),ret.cal_perimeter())
result.display()

tri=Triangle('tri',2,4,5)
result=Shape(tri.n,tri.cal_area(),tri.cal_perimeter())
result.display()

```

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