Python Programming Help for a beginner?

Question

SO I need to find the area of the rectangle. I must put a method in the Rectangle class called "CalcArea()" that multiplies the width * height. I have no clue how to do this and I'm so lost the book doesn't explain how to do this at all. Here's my code:

class Point():
    x = 0.0
    y = 0.0

    def __init__(self, x, y):
        self.x = x
        self.y = y
        print("Point Constructor")

    def ToString(self):
        return "{X:" + str(self.x) + ",Y:" + str(self.y) + "}"

class Ellipse(Point):
    radiusV = 0.0
    radiusH = 0.0

    def __init__(self, x, y, radiusV, radiusH):
        super().__init__(x,y)
        self.radiusV = radiusV
        self.radiusH = radiusH
        print("Ellipse Constructor")

    def ToString(self):
        return super().ToString() + \
                ",{Radius: Vertical = " + str(self.radiusV) + ", Radius: Horizontal = " +     str(self.radiusH) + "}"
p = Point(50,50)
print(p.ToString())
e = Ellipse(80,80,60,80)
print(e.ToString())

class Size():
    width = 0.0
    height = 0.0

    def __init__(self, width, height):
        self.width = width
        self.height = height
        print ("Size Constructor")

    def ToString(self):
        return "{Width = " + str(self.width) + \
               ", Height = " + str(self.height) + "}"

class Rectangle(Point, Size):
    area = 0.0

    def __init__(self, x, y, width, height):
        Point.__init__(self,x,y)
        Size.__init__(self,width,height)
        print("Rectangle Constructor")


    def ToString(self):
        return Point.ToString(self) + "," + Size.ToString(self) + 
s = Size (80,70)
print(s.ToString())

r = Rectangle(200,250,40,50)
print(r.ToString())

Answer 1

In your Rectangle class use the following method

def calcArea(self):
    return self.width * self.height

To print the area simply call print mRectangle.calcArea()

where mRectangle is an instance of the Rectangle class.

self.width and self.height are available to you since Rectangle inherits from Size class and Size has the instance variables width and height set appropriately in its constructor. These values are available to you since Rectangle is a subclass of Size.

Also your width = 0 and height = 0 in Size class might not be doing exactly what you think. They are static or class variables in Python and completely different from self.width and self.height Here is an example to illustrate that

>>> class MyClass():
...     a = 0
...     def __init__(self):
...         self.a = 5
...     def echo(self):
...         print MyClass.a, self.a
... 
>>> instance = MyClass()
>>> instance.echo()
0 5
>>> instance.a
5
>>> MyClass.a
0
>>> 

In python you access class or static variables with the syntax ClassName.Variable and can be accessed without creating an object of that class. Where as an instance variable can be called only with an instance of the class.