On Mon, 16 Feb 2015 08:14:00 -0500, Roy Smith <r...@panix.com> wrote:
>In article <mpg.2f4beb20faeff072989...@nntp.aioe.org>, > Mario Figueiredo <mar...@gmail.com> wrote: > >> It's not been an easy ride trying to decide whether or not to use super. >> I started learning python from a Mark Lutz book that advised me against >> it. > >I'm curious, what were the arguments against it? The following is quoted from Learning Python, 5th Edition: >Java programmers may especially be interested to know that Python also has a >super >built-in function that allows calling back to a superclasss methods more >generically >but its cumbersome to use in 2.X; differs in form between 2.X and 3.X; relies >on unusual >semantics in 3.X; works unevenly with Pythons operator overloading; and does >not >always mesh well with traditionally coded multiple inheritance, where a single >superclass call wont suffice. > >In its defense, the supercall has a valid use case toocooperative same-named >method >dispatch in multiple inheritance treesbut it relies on the MRO ordering of >classes, >which many find esoteric and artificial; unrealistically assumes universal >deployment >to be used reliably; does not fully support method replacement and varying >argument >lists; and to many observers seems an obscure solution to a use case that is >rare in real >Python code. > >Because of these downsides, this book prefers to call superclasses by explicit >name >instead of super, recommends the same policy for newcomers, and defers >presenting >supe until Chapter 32. > [...] >And to any Java programmers in the audience: I suggest resisting the >temptation to use >Pythons superuntil youve had a chance to study its subtle implications. >Once you >step up to multiple inheritance, its not what you think it is, and more than >you probably >expect. The class it invokes may not be the superclass at all, and can even >vary per >context. Or to paraphrase a movie line: Pythons superis like a box of >chocolatesyou >never know what youre going to get! Later, in chapter 32 where super is finally introduced, you can read the following: >As noted in Chapter 28 and Chapter 29, Python has a superbuilt-in function >that can >be used to invoke superclass methods generically, but was deferred until this >point of >the book. This was deliberatebecause superhas substantial downsides in >typical >code, and a sole use case that seems obscure and complex to many observers, >most >beginners are better served by the traditional explicit-name call scheme used >so far. See >the sidebar What About super? on page 831in Chapter 28for a brief summary >of >the rationale for this policy. >The Python community itself seems split on this subject, with online articles >about it >running the gamut from Pythons Super Considered Harmful to Pythons super() >considered super! >Frankly, in my live classes this call seems to be most often of interest >to Java programmers starting to use Python anew, because of its conceptual >similarity >to a tool in that language (many a new Python feature ultimately owes its >existence to >programmers of other languages bringing their old habits to a new model). >Pythons >superis not Javasit translates differently to Pythons multiple inheritance, >and has >a use case beyond Javasbut it has managed to generate both controversy and >misunderstanding since its conception. > >In its defense, this call does have a valid use case toocooperative >same-named method >dispatch in diamond multiple inheritance treesbut it seems to ask a lot of >newcomers. >It requires that superbe used universally and consistently (if not >neurotically), much >like __slots__discussed earlier; relies on the arguably obscure MRO algorithm >to order >calls; and addresses a use case that seems far more the exception than the >norm in >Python programs. In this role, superseems an advanced tool based upon esoteric >principles, >which may be beyond much of Pythons audience, and seems artificial to real >program goals. That aside, its expectation of universal use seems unrealistic >for the vast >amount of existing Python code. -- https://mail.python.org/mailman/listinfo/python-list
