Re: [Python-Dev] isinstance() on old-style classes in Py 2.7

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> Pyth...@python.org> https://mail.python.org/mailman/listinfo/python-dev> Unsubscribe:> https://mail.python.org/mailman/options/python-dev/guido%40python.org>



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