This is one of the unfortunate effects of the existence of "old-style" classes in Python 2. The old-style class hierarchy is distinct from the new-style class hierarchy, but instances of old-style classes are still objects (since in Python, *everything* is an object).
For new code, and whenever you have an opportunity to refactor old code, you should use new-style classes, by inheriting your class from object (or from another class that inherits from object). On Tue, Oct 21, 2014 at 9:43 AM, Andreas Maier <mai...@de.ibm.com> wrote: > > Hi. Today, I ran across this, in Python 2.7.6: > > >>> class C: > ... pass > ... > >>> issubclass(C,object) > False > >>> isinstance(C(),object) > True <-- ??? > > The description of isinstance() in Python 2.7 does not reveal this result > (to my reading). > > From a duck-typing perspective, one would also not guess that an instance > of C would be considered an instance of object: > > >>> dir(C()) > ['__doc__', '__module__'] > >>> dir(object()) > ['__class__', '__delattr__', '__doc__', '__format__', '__getattribute__', > '__hash__', '__init__', '__new__', '__reduce__ > ', '__reduce_ex__', '__repr__', '__setattr__', '__sizeof__', '__str__', > '__subclasshook__'] > > -> What is the motivation for isinstance(C,object) to return True in Python > 2.7? > > Andy > > Andreas Maier > IBM Senior Technical Staff Member, Systems Management Architecture & Design > IBM Research & Development Laboratory Boeblingen, Germany > mai...@de.ibm.com, +49-7031-16-3654 > ________________________________________________________________________ > IBM Deutschland Research & Development GmbH > Vorsitzende des Aufsichtsrats: Martina Koederitz > Geschaeftsfuehrung: Dirk Wittkopp > Sitz der Gesellschaft: Boeblingen > Registergericht: Amtsgericht Stuttgart, HRB 243294 > > _______________________________________________ > Python-Dev mailing list > Python-Dev@python.org > https://mail.python.org/mailman/listinfo/python-dev > Unsubscribe: > https://mail.python.org/mailman/options/python-dev/guido%40python.org > -- --Guido van Rossum (python.org/~guido)
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