I've been trying to write a Python C extension module that uses NumPy
and has a subtype of numpy.ndarray written in C. However, I've run into
a snag: calling numpy.ndarray.__new__(mysubtype, ...) triggers an
exception in the bowels of Python (this is necessary for a handful of
NumPy features). I'm posting to this list to try to figure out why this
exception exists in the first place, and what (if anything) I can do to
work around it.
The exception in question happens in Objects/typeobject.c in
tp_new_wrapper. Here's the comment for the block:
/* Check that the use doesn't do something silly and unsafe like
object.__new__(dict). To do this, we check that the
most derived base that's not a heap type is this type. */
The code has the end effect that basetype.__new__(subtype, ...) fails
whenever subtype is a statically-defined type (i.e. a normal C extension
type object). Why is this necessary in general? I can see why it might
be bad for a limited number of core Python types, but it seems
unnecessarily limiting for Python C extensions.
On a more practical note, is there a way (short of rewriting the subtype
in Python) to work around this? It seems that I could call the type
metaclass to create a heap type in C, but I'm not sure of all the
implications of that.
Thanks in advance,
Jim
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