Tom Whittock, 27.06.2011 12:48:
I'm writing a module to proxy C++ objects into Python for a large C++ application. There are hundreds of thousands of C++ objects, some of which are temporary while others are very long lived.
Currently every time one of these objects is accessed from Python, a new "myproxy" instance is created. So if I were to access the same field of an object twice, I would receive two python objects proxying the same underlying C++ object. This messes up "id" and "is"
Note that "is" actually compares the addresses, not the id().
and is causing me issues when, for example, I run into circular references when enoding json or otherwise attempt to determine whether two proxy objects refer to the same C++ object.
I can't see how to cache the "myproxy" objects instead of returning new instances - due to the architecture of the C++ application, there's no weak reference support at all, and the number of objects is very large.
My current plan would be for me to override the id builtin to return the underlying C++ object instance pointer instead of the PyObject instance pointer in the case of the "myproxy" object type
Where would you get the proxy object from anyway? IMHO, there are two obvious way get what you want: map the C++ object address (integer!) to a proxy object using a dict, or use a backpointer from the C++ object to its proxy. The second is substantially faster, but may require changes to the C++ class struct. I don't see how changes to CPython's core can help you here. Stefan