At 10:36 PM 5/13/2007 -0700, Collin Winter wrote: >2. Querying instances :: > > if performs(my_elf, Thieving): > ...
-1 on using any function other than isinstance() for this. Rationale: isinstance() makes the code smell of inspection more obvious, where another function name makes it seem like you are doing something harmless. In reality, performs() testing (or any other kind of interface testing) using if-then is always harmful in library code. > The second argument to ``performs()`` may also be anything with a > ``__contains__()`` method, meaning the following is legal: :: > > if performs(my_elf, set([Thieving, Spying, BoyScout])): > ... > > Like ``isinstance()``, the object needs only to perform a single > role out of the set in order for the expression to be true. Right, so let's just use isinstance(). Likewise, issubclass() for checking whether instances of a class perform a role. (And if issubclass() works, then roles will also be usable by PEP 3124 generic functions without any additional effort.) _______________________________________________ Python-3000 mailing list Python-3000@python.org http://mail.python.org/mailman/listinfo/python-3000 Unsubscribe: http://mail.python.org/mailman/options/python-3000/archive%40mail-archive.com
