> I don't understand how the function ended up with func_code=NULL. That shouldn't be a valid function to call, IMO. Do you have any info on how the function ended up in that state?

It doesn't seem possible to create a function with func_code=NULL, nor to set func_code to NULL. func_code can be be set to NULL by func_clear() which is called by func_dealloc().

I bet that func_clear() has been called since most func fields are set to NULL, which is consistent with:

static int
func_clear(PyFunctionObject *op)
{
    Py_CLEAR(op->func_code);
    Py_CLEAR(op->func_globals);
    Py_CLEAR(op->func_module);
    Py_CLEAR(op->func_name);
    Py_CLEAR(op->func_defaults);
    Py_CLEAR(op->func_kwdefaults);
    Py_CLEAR(op->func_doc);
    Py_CLEAR(op->func_dict);
    Py_CLEAR(op->func_closure);
    Py_CLEAR(op->func_annotations);
    Py_CLEAR(op->func_qualname);
    return 0;
}

The question is how is it possible that a deallocated function is still accessed? It smells like a borrowed reference somewhere in the call chain.