Rob Cliffe <rob.cli...@btinternet.com> added the comment: On 14/07/2018 13:44, Nick Coghlan wrote: > Nick Coghlan <ncogh...@gmail.com> added the comment: > > Reviewing the builtins in 3.7, I get the following results for builtin > objects that have defined subclasses immediately after interpreter startup: > > ============= >>>> for name, obj in vars(builtins).items(): > .. if isinstance(obj, type) and name in str(obj): > .. subclasses = type(obj).__subclasses__(obj) > .. if subclasses: > .. print(f"{obj}: {len(subclasses)}") > .. > <class 'classmethod'>: 1 > <class 'dict'>: 1 > <class 'property'>: 1 > <class 'int'>: 1 > <class 'object'>: 132 > <class 'staticmethod'>: 1 > <class 'tuple'>: 16 > <class 'type'>: 1 > <class 'BaseException'>: 4 > <class 'Exception'>: 19 > <class 'ImportError'>: 2 > <class 'OSError'>: 13 > <class 'RuntimeError'>: 3 > <class 'NameError'>: 1 > <class 'SyntaxError'>: 1 > <class 'IndentationError'>: 1 > <class 'LookupError'>: 3 > <class 'ValueError'>: 2 > <class 'UnicodeError'>: 3 > <class 'ArithmeticError'>: 3 > <class 'SystemError'>: 1 > <class 'Warning'>: 10 > <class 'ConnectionError'>: 4 > ============= > > So rather than special-casing exceptions or builtins in general, my > inclination would be to include a section that lists up to 4 subclasses > inline, and then adds a "... and NNN additional subclasses" trailing when > there are more than 4 (or when there are less than 4 subclasses with public > names, but additional private subclasses). > > My 2 cents: To use Exceptions optimally (e.g. to make the errors you trap neither too specific nor too general), you often need to know (and understand) the relevant part of the Exception hierarchy. In particular you may know the name of an Exception that covers a particular use case, but not the names of its subclasses, one of which might be more appropriate. Exceptions are exceptional* in that the "issubclass" relationship is vital to the way that they work. So it is USEFUL to know ALL subclasses of a given Exception class (not just 4; in practice there won't be more than a dozen or two). I have found myself in just this position; in fact it impelled me to adding a "show subclasses" feature to help(<anyExceptionClass>) in my then current version of Python 2. (An alternative might be a handy way of showing the complete built-in Exception hierarchy.)
I question whether it is really useful to know all subclasses of ANY class, or whether YAGNI. I think that, for non-Exception classes, typically when you look at a class you may want to know its inheritance (to understand its functionality better), but it is rare that you will want to know what subclasses it has, if any. No doubt there are exceptions* (perhaps you monkey-patch a class and want to know what subclasses might be affected). Regards Rob Cliffe * Pun not intended ---------- _______________________________________ Python tracker <rep...@bugs.python.org> <https://bugs.python.org/issue8525> _______________________________________ _______________________________________________ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com