How to assign a data attribute of a subclass to attributes of its parent class

Question

I have a class Rectangle with data attributes width and height, I want a subclass Square with data attribute side_length.

How do I make it so that square.width and square.height give its side length? i.e same as square.side

class Rectangle:
    def __init__(self, width, height):
        self.width = width
        self.height = height

class Square(Rectangle):
    def __init__(self, side)
        self.side = side

This is what I have so far.

Answer 1

You could call the constructor for Rectangle.

super(Square,self).__init__(side, side)

or you could have properties to return those attributes. I'd edge towards the super.

@property
def length(self):
   return self.side

@property
def width(self):
   return self.side

Things get more complicated if you can change the side, height or width attribute after creating the object. You need to keep width and height synched and coherent. One possible way is to do away entirely with side as a stored attribute on Square and instead have it as a read-write property that updates Rectangle's width and height.

to keep height/width/side sorted after the initial constructors:

class Rectangle:

    @property
    def height(self):
        return self._height

    @height.setter
    def height(self, value):
        self._height = value

    @property
    def width(self):
        return self._width

    @width.setter
    def width(self, value):
        self._width = value

    def __repr__(self):
        return(f"{self.__class__.__name__}:{self.height=} {self.width=}")

    def __init__(self, height, width):
        self.height = height
        self.width = width

class Square(Rectangle):

    def __repr__(self):
        return(f"{self.__class__.__name__}:{self.side=}")

    @property
    def side(self):
        return self._width

    @side.setter
    def side(self, value):
        self._width = value
        self._height = value

    def __init__(self, side):
        super(Square, self).__init__(side, side)

    #these are here so you can't cheat and vary height and width
    #independently on a square
    @property
    def width(self):
        return self.side

    @width.setter
    def width(self, value):
        self.side = value

    @property
    def height(self):
        return self._side

    @height.setter
    def height(self, value):
        self.side = value



rectangle = Rectangle(5,2)
print(rectangle)
rectangle.height = 6
print(rectangle)

square = Square(3)
print(square)
square.side = 6
print(square)
square.height = 9
print(square)

output:

$ py test_square.py
Rectangle:self.height=5 self.width=2
Rectangle:self.height=6 self.width=2
Square:self.side=3
Square:self.side=6
Square:self.side=9