Antoine Pitrou <[email protected]> added the comment:
> My patch attempts to emulate 2.x PyInstance_NewRaw with a call to
> tp_alloc.
This is certainly the wrong thing to do. You could at least try
PyBaseObject_Type.tp_new (see object_new() in typeobject.c), but even this is
not necessarily right (for example if the class is derived from an extension
type defining its own tp_new).
So, IMO, the right thing to do would be to choose the first base type that
isn't a Python-defined class and use its tp_new:
staticbase = subtype;
while (staticbase && (staticbase->tp_flags & Py_TPFLAGS_HEAPTYPE))
staticbase = staticbase->tp_base;
(these two lines are from tp_new_wrapper() in typeobject.c)
That way you choose the right constructor function, yet don't call the
Python-defined __new__ function. That's the only reasonable way of doing it I
can imagine. It also follows the following behaviour:
>>> class C(int):
... def __new__(cls, *a):
... print "__new__", a
... return int.__new__(cls, *a)
...
>>> C(5)
__new__ (5,)
5
>>> s = pickle.dumps(C(5))
__new__ (5,)
>>> x = pickle.loads(s)
>>> x
5
As you can see, int.__new__ has been called on unpickling but not C.__new__ (no
print).
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<http://bugs.python.org/issue5180>
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