Why do Python functions get garbage collected?

I have a C++ library which uses Python call开发者_开发问答backs. The callback, i.e. PyObject*, is stored in an object of class UnaryFunction, and the constructor Py_INCREFs it. The destuctor Py_XDECREFs it. That's the problem. The interpreter segfaults on that DECREF.

My solution is to just not DECREF it, but that seems wrong. What is the proper way to INC/DEC the reference count of a function, and more importantly, why does the interpreter try to GC a function body when there are other live references to it?

Edit: On Linux instead of a segfault I get an assertion fail that says:

python: Objects/funcobject.c:442: func_dealloc: Assertion 'g->gc.gc_refs != (-2)' failed.

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A crash does not necessary mean that it is trying to GC an used object. It can also mean that you are calling python code without the interpretor lock.

Calling Py_XDECREF in a destructor leads me to think you have something like this:

void MyCallback(myfunc, myarg)
{
    ...
    PyGILState_STATE gilstate = PyGILState_Ensure();
    try {
            myfunc(myarg);
    } catch (...) {
        ...
    }
    PyGILState_Release(gilstate);

    // myfunc goes out of scope here --> CRASH because we no longer own the GIL
}

with the simple solution:

...
try {
    scopefunc = myfunc;
    myfunc = emptyfunc();
    scopefunc(myarg);
} ...

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It appears the Py_INCREF simply doesn't actually increment the refcount.