Christoph, Do you realize that __xxx__ names can have any semantics they darn well please? If a particular __xxx__ name (or some aspect of it) is undocumented that's not a bug (not even a doc bug), it just means "hands off".
That said, there may well be a bug, but it would be in the behavior of those things that *are* documented. --Guido On Sat, Aug 6, 2011 at 7:55 AM, Christoph Groth <c...@falma.de> wrote: > Hi, > > while playing with abstract base classes and looking at their > implementation, I've stumbled across the following issue. With Python > 3.2, the script > > class Foo(object): > __abstractmethods__ = ['boo'] > class Bar(object): > pass > Bar.__abstractmethods__ = ['boo'] > f = Foo() > b = Bar() > > produces the following output > > Traceback (most recent call last): > File "/home/cwg/test2.py", line 9, in <module> > b = Bar() > TypeError: Can't instantiate abstract class Bar with abstract methods buzz > > This seems to violate PEP 3119: it is not mentioned there that setting > the __abstractmethods__ attribute already during class definition (as in > "Foo") should have no effect. > > I think this happens because CPython uses the Py_TPFLAGS_IS_ABSTRACT > flag to check whether a class is abstract. Apparently, this flag is not > set when the dictionary of the class contains __abstractmethods__ > already upon creation. > > As a second issue, the special __abstractmethods__ attribute (which is a > feature of the interpreter) is not mentioned anywhere in the > documentation. > > If these are confirmed to be bugs, I can enter them into the issue > tracker. > > Christoph > > _______________________________________________ > 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/guido%40python.org > -- --Guido van Rossum (python.org/~guido) _______________________________________________ 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
