python: pickling c objects

Question

First off I'm not expecting a solution, just hoping for some pointers on how to start.

I've got a C program with an embedded Python interpreter. The Python scripts the program uses as input obviously refer to the C-defined objects and functions. I'd now like to make some of these objects pickleable.

The pickle docs describe how extension types can be made picklable using __reduce__. But this is a Python method - how would I define this in the underlying PyObject?

Fairly sure I'm mis-understanding something...

Answer 1

The pickle module comes in both a python-only and a C variant (called cPickle). As such, the __reduce__ method needs to be callable from Python code.

Thus, you need to provide a __reduce__ entry in your C object PyMethodDef struct with a suitable implementation.

Alternatively, you can also register a pickling function with the copy_reg module. This module's original usecase was to support extension modules better; the source code for the module states:

This is only useful to add pickle support for extension types defined in C, not for instances of user-defined classes.