[Python-Dev] How to suppress instance dict? (original) (raw)

David Abrahams dave@boost-consulting.com
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" <joel@boost-consulting.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" outx = pickle.dumps(x) print "LOADING" xl = pickle.loads(outx) 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 tpnew of PyTypeObject. How do I call the default tpnew for metaclasses?

PyTypeObject.tp_new( /args here/ ) should work.

HTH,

-- Dave Abrahams Boost Consulting www.boost-consulting.com