[Jython-users] isinstance() and issubclass() - inconsistant results

[Charles D. <cd...@sp...>]

G'day. I've encountered a situation where issubclass() reports that an item's
class is a subclass of a given parent class, yet isinstance() reports that the
item is not an instance of that parent class. To demonstrate:

---- Correct behaviour
>>> class A: pass
... 
>>> class B(A): pass
... 
>>> isinstance(B(), A)
1
>>> issubclass(B,A)
1
---- Observed Incorrect behaviour
>>> print item.__class__
com.wutka.dtd.DTDSequence
>>> isinstance(item, DTDItem)
0
>>> issubclass(DTDSequence, DTDItem)
1
>>> issubclass(item.__class__, DTDItem)
1



I'm using Jython 2.1 (from version 2.1.0-8 of the debian jython package) on a
Sun JRE (1.4.1_01) with no JIT enabled. The DTD parsing library which this is
occuring with is available at http://www.wutka.com/dtdparser.html; the javadocs
are available from http://www.wutka.com/dtdparserapi/index.html.

Any insight you might be able to provide into why this could be occuring would
be greatly appreciated. Thanks!