On Tue, Nov 4, 2014 at 12:50 AM, Dennis Lee Bieber <wlfr...@ix.netcom.com> wrote: > On Mon, 3 Nov 2014 03:12:32 +0000 (UTC), Denis McMahon > <denismfmcma...@gmail.com> declaimed the following: > >>So: >> >>Quadrilateral >> Parallelogram >> Square >> Rectangle >> Rhombus >> Diamond (4 sides eq) >> Trapezoid >> Arrowhead >> >>Is an arrowhead a trapezoid? > > I'd probably indent square under rectangle, and indent diamond where > it > is -- both being restrictions on rectangle/rhombus > > But we may need another category, convex and concave; the arrowhead > would fall into the concave grouping.
That's fine if you're creating a taxonomical hierarchy of immutables, but neither works if you're creating a mutable class hierarchy that follows LSP. The only way you can make any of this work (as someone suggested earlier, I believe) is by having __new__ potentially return a subclass, so if you ask Parallelogram to give you one with all sides equal and all angles equal, it gives you back a Square. But since a square is a special form of rhombus as well as a special form of rectangle, you'd have to use multiple inheritance or an AST-style subclass hook to verify. Of course, if you're going down that route, you probably want to take this up a level and have a Shape class, and have the subclass hook simply check if it's four-sided as well. ChrisA -- https://mail.python.org/mailman/listinfo/python-list
