Guido van Rossum wrote: > I'm asking a Py3k question on python-dev because I'd like to have > opinions from people who haven't thought about Py3k much yet. Consider > the following example: > > class C: > def foo(self): pass > > C.foo(42) > > This currently fails with this error message: > > TypeError: unbound method foo() must be called with C instance as > first argument (got int instance instead) > > This message is called when isinstance(self, C) returns False, where > self is the first argument passed to the unbound method. > > That's nice, but there is a cost associated with this: the expression > "C.foo" can't just return the function object "foo", it has to wrap it > in an unbound method object. In Py3k the cost of calling an unbound > method object goes up, because the isinstance() check may be > overloaded. This typically happens when the class C uses the special > metaclass (abc.ABCMeta) used for virtual inheritance (see PEP 3119). > in Py3k the I/O stream classes are perhaps the most common use case.
Could we check for "real" inheritance first, and call __instancecheck__ only when the previous is false? It would speed-up the common cases. Or is there really a use case for a derived class to appear as NOT being a subclass of its base class? -- Amaury Forgeot d'Arc _______________________________________________ Python-Dev mailing list Python-Dev@python.org http://mail.python.org/mailman/listinfo/python-dev Unsubscribe: http://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
