15.6 从C语言中调用Python代码.pdf

15.6 从C语⾔中调⽤Python代码 问题 You want to safely execute a Python callable from C and return a result back to C . Forexample , perhaps you are writing C code that wants to use a Python function as acallback . 解决⽅案 Calling Python from C is mostly straightforward , but involves a number of tricky parts.The following C code shows an example of how to do it safely include / Execute f unc(x ,y) in the Python interp reter . Thearguments and return result of the f unction mustbe Python f loats [](#)/double call_func(PyObject *func , double x , double y) { PyObject *args;PyObject *kwargs;PyObject *result = 0;double retval; / Make sure e o n the GIL [](#)/PyGILState_STATE state = PyGILState_Ensure(); / Verif y that f unc is a p rop er callable [](#)/if ( !PyCallable_Check(func)) { fprintf(stderr ,”call_func expected a callablen”);goto fail; }/ Build arguments [](#)/args = Py_BuildValue(“(dd)”, x , y);kwargs = NULL; / Call the f unction [](#)/result = PyObject_Call(func , args, kwargs);Py_DECREF(args);Py_XDECREF(kwargs); / Check f or Python excep tions (if any) [](#)/if (PyErr_Occurred()) { PyErr_Print();goto fail; } / Verif y the result is a f loat obj ect [](#)/if ( !PyFloat_Check(result)) { fprintf(stderr ,”call_func callable didnt return a floatn”);goto fail; } / Create the return value [](#)/retval = PyFloat_AsDouble(result);Py_DECREF(result); / Restore p revious GIL state and return [](#)/PyGILState_Release(state);return retval; fail Py_XDECREF(result);PyGILState_Release(state);abort(); // Change to something more appropriate } To use this function , you need to have obtained a reference to an existing Python callableto pass in . There are many ways that you can go about doing that , such as having acallable object passed into an extension module or simply writing C code to extract asymbol from an existing module .Here is a simple example that shows calling a function from an embedded