[Python-bugs-list] [ python-Bugs-409355 ] Meta-class inheritance problem
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Wed, 21 Mar 2001 11:18:06 -0800
Bugs item #409355, was updated on 2001-03-17 02:10
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Category: Python Interpreter Core
>Group: Feature Request
>Status: Closed
Priority: 7
Submitted By: Lorien Dunn (loriend)
Assigned to: Guido van Rossum (gvanrossum)
Summary: Meta-class inheritance problem
Initial Comment:
I've run into a bug in python 2.0. The real code that
the following pseudo code represents throws a
TypeError.
class MyDerivedClass(MyPurePythonClass,MyBoostClass):
def __init__(self):
MyPurePythonClass.__init__(self)
MyBoostClass.__init__(self)
The problem occurs in MyPurePythonClass- Python says
"unbound method must be called with class instance 1st
argument". This makes sense: I'm passing a meta-class
instead of a class. David Abrahams (the main author of
boost::python) agrees that this is a Python problem,
and that it should affect Zope as well.
I think I've found the point in the python 2.0 sorce
where it occurs:
ceval.c, line 1816 (reformatted for clarity):
/* BEGIN CODE SAMPLE */
else
{
/* Unbound methods must be called with an instance of
the class (or a derived class) as first argument */
if (na > 0 && (self = stack_pointer[-n]) != NULL
&& PyInstance_Check(self)
&& PyClass_IsSubclass((PyObject
*) (((PyInstanceObject*) self)->in_class),
class))
/* Handy-dandy */ ;
else
{
PyErr_SetString(PyExc_TypeError, "unbound
method must be called with class instance 1st
argument");
x = NULL;
break;
}
}
/* END CODE SAMPLE */
----------------------------------------------------------------------
>Comment By: Guido van Rossum (gvanrossum)
Date: 2001-03-21 11:18
Message:
Logged In: YES
user_id=6380
I *think* I've fixed this now -- please test with the
current CVS.
Please let me know if I goofed up, and I'll reopen the bug
report.
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Comment By: Guido van Rossum (gvanrossum)
Date: 2001-03-18 14:22
Message:
Logged In: YES
user_id=6380
Zope has several workarounds, so isn't affected.
But I agree it could be fixed. The test is there because it wants to enforce a concept: 'self' should be an instance
of the class that defines the method (where a subclass instance is fine too).
But the implementation of the test is based too much on the default implementation of classes.
Could someone please submit a patch that replaces the concrete isinstance() test with an isinstance() test similar
to that in bltinmodule.c? (Maybe we need to add a new C API, PyObject_IsInstance().)
If someone could come up with a check that conve
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Comment By: David Abrahams (david_abrahams)
Date: 2001-03-18 05:30
Message:
Logged In: YES
user_id=52572
Sorry, that anonymous comment is mine. I'm still a bit
clumsy with SourceForge.
-Dve
----------------------------------------------------------------------
Comment By: Nobody/Anonymous (nobody)
Date: 2001-03-18 05:03
Message:
Logged In: NO
I was a bit surprised to learn that this check was still in
the code after issubclass and isinstance had been fixed to
work with extension classes. Suppose you checked for a
__class__ attribute on the first argument instead (or
additionally)?
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Comment By: Tim Peters (tim_one)
Date: 2001-03-17 21:29
Message:
Logged In: YES
user_id=31435
Assigned to Guido, because I bet JimF would refuse to take
blame for this <wink>.
----------------------------------------------------------------------
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