[Tutor] Multiple inheritance - Need clarity

[Dennis Lee Bieber]

	o/~ Talking to myself in public o/~

On Fri, 26 Nov 2021 22:14:18 -0500, Dennis Lee Bieber
<wlfraed at ix.netcom.com> declaimed the following:

>	Personally, I would not use inheritance for this example but
>composition.
>

	To better clarify...

	Inheritance is used if/when the subclass IS also a parent class

	A Cylinder is NOT a Circle, NOR is it a Rectangle.

Class Carnivore():
	...

Class Mammal():
	...

Class Fish():
	...

Class Cat(Mammal, Carnivore):
	...

Class Shark(Fish, Carnivore):
	...

	A Cat IS A Mammal.
	A Cat IS also A Carnivore.

	A Shark IS A Fish.
	A Shark IS also A Carnivore.

	Composition is used when the class is made up of other objects.

	A Cylinder HAS A Circle (actually, two identical for top and bottom), A
Cylinder also HAS A Rectangle (using your style for the column)

Class Vehicle():
	...

Class Wheel():
	...

Class Engine():
	...

Class InternalCombustion(Engine):
	#internal combustion IS A engine

Class Diesel(Engine):
	#similarly

Class PassengerCar():
	def __init__(self, engine):
		self.wheels = { "LF" : Wheel(...),
					"RF": Wheel(...),
					"LR" : Wheel(...),
					"RR" : Wheel(...)	]
		self.engine = engine

	A PassengerCar HAS multiple Wheels, a PassengerCar HAS an engine.
(some sports cars may have larger rear tires than front tires -- I've only
hinted that this could be the case her -- would have to add parameters to
__init__ to allow for such.


	Personally, I wouldn't even use composition for your Cylinder() -- I'd
just save radius and height directly, rather than the indirect radius (in
Circle()) and height/width (in Rectangle) -- do you expect anyone to ask
for
	cylinder.rectangle.width
?
I'd think anyone working with a cylinder would be more likely to ask for
	cylinder.radius
	cylinder.height
NOT
	cylinder.circle.radius
	cylinder.rectangle.height
(who thinks of /rectangles/ when discussing a cylinder?) Even worse, your
rectangle just has side1 and side2 -- how does a user know which is the
height, and which is the width?


-- 
	Wulfraed                 Dennis Lee Bieber         AF6VN
	wlfraed at ix.netcom.com    http://wlfraed.microdiversity.freeddns.org/