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To: python-list@python.org
From: Dennis Lee Bieber <wlfraed@ix.netcom.com>
Subject: Re: Classes
Date: Sat, 01 Nov 2014 12:00:46 -0400
Organization: IISS Elusive Unicorn
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On Fri, 31 Oct 2014 19:32:13 -0400, Seymore4Head
<Seymore4Head@Hotmail.invalid> declaimed the following:

>
>class Rectangle(object):
>    def __init__(self, length, width=None):
>        self.length = length
>        if width is None:
>            self.width = length
>        else:
>            self.width = width
>    def area(self):
>        return self.length * self.width
>    def perimeter(self):
>        return 2 * (self.length + self.width)
>
>class Square(Rectangle):
>    def area(self):
>        return self.length * self.width
>    def perimeter(self):
>        return 2 * (self.length + self.width)    
>
	Why did you redefine area and perimeter? Those are supposed to be
inherited operations from Rectangle. You've duplicated what should not have
been changed, and removed everything that makes a Square a Square.

	The "assignment" was to create a Square class that enforces the
property of "squareness" (length = width, or a simple "side").

	What you created does not do that.
    
>a=Rectangle(3,5)
>print (a.area())
>print (a.perimeter())
>b=Rectangle(5,7)
>print (b.area())
>print (b.perimeter())
>c=Square(4)
>print (c.area())
>print (c.perimeter())

	You're tests ignore the case of /changing/ side/length/width...
Consider what happens if you execute

c.length = 5
c.width = 9

	Your "square" is now a rectangle... My example forces every change to a
"Square" to affect both dimensions equally -- no matter if you set .side,
.length, .width, the square will still be a square.
-- 
	Wulfraed                 Dennis Lee Bieber         AF6VN
    wlfraed@ix.netcom.com    HTTP://wlfraed.home.netcom.com/