[Python-Dev] How to suppress instance __dict__?
Wed, 02 Apr 2003 07:57:34 -0500
Hi, Joel --
I don't think this is more than marginally appropriate for python-dev,
and probably we shouldn't bother Guido about it until I've failed to
help you first. Everybody else can ignore the rest of this message
unless they have a sick fascination with Boost.Python...
"Joel de Guzman" <email@example.com> writes:
> Ok, I'm lost. Please be easy with me, I'm still learning the C API
> interfacing with Python :) Here's what I have so far. Emulating the
> desired behavior in Python, I can do:
> class EnumMeta(type):
> def __new__(cls, name, bases, dict):
> C = type.__new__(cls, name, bases, dict)
> del C.__getstate__
> return C
> class Enum(int):
> __metaclass__ = EnumMeta
> __slots__ = ()
> x = Enum(1964)
> print x
> import pickle
> print "SAVING"
> out_x = pickle.dumps(x)
> print "LOADING"
> xl = pickle.loads(out_x)
> print xl
> I'm trying to rewrite this in C/C++ with the intent to patch
> Boost.Python to allow pickling on enums. I took on this task to
> learn more about the low level details of Python C interfacing.
> So far, I have implemented EnumMeta in C that does not override
> anything yet and installed that as the metaclass of Enum.
> I was wondering... Is there some C code somewhere that I can see
> that implements some sort of meta-stuff?
We have some in Boost.Python already, and I'm about to check in some
more to implement static data members.
> I read PEP253 and 253 and "Unifying Types and Classes in Python
> 2.2". The examples there (specifically the class autoprop) is
> written in Python. I tried searching for examples in C from the
> current CVS snapsot of 2.3 but I failed in doing so. I'm sure it's
> there, but I don't know where to find.
Actually there are very few metaclasses in Python proper. AFAIK,
PyType_Type is the only metaclass in the core.
> To be specific, I'm lost in trying to implement tp_new of
> PyTypeObject. How do I call the default tp_new for metaclasses?
PyTypeObject.tp_new( /*args here*/ ) should work.