How to remove a Python function from a module using C++? - c++

Question

Creating an application in C++, I integrated CPython to facilitate the development of certain top-level logics.
The application has a plugin subsystem, which can loaded/unloaded plugins at runtime, this implies to add and remove Python definitions at runtime.
I found that I can add functions with PyModule_AddFunctions, and similarly, I can add constants, objects, etc...
But I found no equivalent PyModule_RemoveFunction.
How to remove a Python function from a module using C++?
Note: Ideally, I would like to avoid solutions like:
Removing the full module and reloading everything
Crafting Python code, that when executed would remove the function.
Let see an example:
DISCLAIM: I removed most of the error checks for simplicity.
#define PY_SSIZE_T_CLEAN
#include <Python.h> //before std includes
// Just an example function to add/remove from Python
static PyObject* log(PyObject* , PyObject* args)
{
//Do something
Py_INCREF(Py_None);
return Py_None;
}
// Setup a "AppModule" module
PyMODINIT_FUNC initAppModule()
{
static PyModuleDef AppModuleInfo{
PyModuleDef_HEAD_INIT,
"AppModule", // name of module
nullptr, // module documentation, may be NULL
-1, // size of per-interpreter state of the module, or -1 if the module keeps state in global variables.
nullptr
};
const auto AppModule = PyModule_Create(&AppModuleInfo);
PyModule_AddFunctions(AppModule, AppModuleMethods);
return AppModule;
}
// Adding a function when a plugin is loaded
void PluginAddingAFunction()
{
static PyMethodDef AppModuleMethods[]{
{"log", log, METH_VARARGS,
"Log a message in the standard output."},
{NULL, NULL, 0, NULL} // Sentinel
};
PyObject *modName = PyUnicode_FromString("AppModule");
PyObject *mod = PyImport_Import(modName);
PyModule_AddFunctions(mod, AppModuleMethods);
}
// Removing the function when the plugin is unloaded
void PluginRemoveAFunction()
{
PyObject *modName = PyUnicode_FromString("AppModule");
PyObject *mod = PyImport_Import(modName);
// How to do this?
//PyModule_RemoveFunctions(mod, "log");
}
int main(int argn, const char* argv[])
{
Py_SetProgramName(argv[0]);
PyImport_AppendInittab("AppModule", &initAppModule);
Py_Initialize();
PyObject *pmodule = PyImport_ImportModule("AppModule");
PluginAddingAFunction(); // <<===== This is done at any time, when loading a plugin
PyRun_SimpleString("import AppModule\n"
"AppModule.log('Hi World')\n"); // <== Example code
PluginRemoveAFunction(); // <<===== This is done when unloading a plugin
Py_FinalizeEx();
}

Answer 1

You can use PyObject_DelAttr C-apis.
int PyObject_DelAttr(PyObject *o, PyObject *attr_name)
Delete attribute named attr_name, for object o. Returns -1 on failure. This is the equivalent of the Python statement del o.attr_name
Reference.
So you could do something like this to remove log function
void PluginRemoveAFunction()
{
PyObject *modName = PyUnicode_FromString("AppModule");
PyObject *mod = PyImport_Import(modName);
PyObject *funcName = PyUnicode_FromString("log");
PyObject_DelAttr(mod, funcName);
}