PythonからCの関数を呼び出す（Cの関数の共有ライブラリ化） Part2
どうも，筆者です．
前回のつづきになる．
workspacememory.hatenablog.com
今回は，二つの配列の和，差，積を計算し，与えられた配列に結果を格納する関数をPythonから呼び出せるようにする．
Pythonで受け付けるオブジェクト型はlist型のみとする．
以下のサイトを参考にした．
Cの関数定義
前回のコードに追加する形で実装していく．
ヘッダー
ヘッダーファイルの内容を以下に示す．
// custom.h #ifndef CUSTOM_H__ #define CUSTOM_H__ #include <stdint.h> extern int32_t add(int32_t x, int32_t y); extern void set_value(int32_t val); extern double newton_method(double x0, int32_t max_iter, double (*target_func)(double x)); // 追加部分 extern int32_t calc_array(int32_t len, char oprator, const double *left_term, const double *right_term, double *out); // ここまで #endif
関数
#include <stdint.h> // 追加部分1 #include <stddef.h> // ここまで #include "custom.h" #define DELTA (1e-3) static int32_t g_val = 0; int32_t add(int32_t x, int32_t y) { int32_t z; z = x + y + g_val; return z; } void set_value(int32_t val) { g_val = val; } double newton_method(double x0, int32_t max_iter, double (*target_func)(double x)) { int32_t iter; double old_x, new_x, df; new_x = x0; for (iter = 0; iter < max_iter; iter++) { old_x = new_x; df = ((*target_func)(old_x + (double)DELTA) - (*target_func)(old_x - (double)DELTA)) / (double)DELTA * 0.5; new_x = old_x - (*target_func)(old_x) / df; } return new_x; } // 追加部分2 int32_t calc_array(int32_t len, char operator, const double *left_term, const double *right_term, double *out) { int32_t ret = 1; int32_t idx; if ((NULL != left_term) && (NULL != right_term) && (NULL != out)) { ret = 0; switch((int)operator) { case ((int)'+'): for (idx = 0; idx < len; idx++) { out[idx] = left_term[idx] + right_term[idx]; } break; case ((int)'-'): for (idx = 0; idx < len; idx++) { out[idx] = left_term[idx] - right_term[idx]; } break; case ((int)'*'): for (idx = 0; idx < len; idx++) { out[idx] = left_term[idx] * right_term[idx]; } break; default: ret = 1; break; } } return ret; } // ここまで
Wrapper関数定義
Pythonで呼び出す際は，演算子と二つのリストを与え，結果をリスト形式で返す方式とする． また，ネストが深くなるため，所々で例外処理も実装している．
#include <stdint.h> #include "Python.h" #include "custom.h" PyObject *wrapper_add(PyObject *self, PyObject *args) { int32_t x, y, z; PyObject *ret = NULL; if (PyArg_ParseTuple(args, "ii", &x, &y)) { z = add(x, y); ret = Py_BuildValue("i", z); } return ret; } PyObject *wrapper_set_value(PyObject *self, PyObject *args) { int32_t val; PyObject *ret = NULL; if (PyArg_ParseTuple(args, "i", &val)) { set_value(val); ret = Py_BuildValue(""); } return ret; } static PyObject *py_object_function = NULL; static double alternative_obj_func(double x) { double ret_val = x; PyObject *arg, *result; // set argument arg = Py_BuildValue("(d)", x); // call function result = PyEval_CallObject(py_object_function, arg); // check result if (result && PyFloat_Check(result)) { ret_val = PyFloat_AsDouble(result); } Py_XDECREF(result); Py_DECREF(arg); return ret_val; } PyObject *wrapper_newton_method(PyObject *self, PyObject *args) { double x0; double est_x; int32_t max_iter; PyObject *target_func = NULL; PyObject *ret = NULL; if (PyArg_ParseTuple(args, "diO", &x0, &max_iter, &target_func)) { if (!PyCallable_Check(target_func)) { PyErr_SetString(PyExc_TypeError, "Need a callable object!"); } else { // set function pointer Py_INCREF(target_func); Py_XDECREF(py_object_function); py_object_function = target_func; // call function est_x = newton_method(x0, max_iter, alternative_obj_func); ret = Py_BuildValue("d", est_x); } } return ret; } // 追加部分1 PyObject *wrapper_calc_array(PyObject *self, PyObject *args) { int32_t idx; int32_t return_code; int size; char operator; double *work_left, *work_right, *work_out; PyObject *left_term, *right_term; PyObject *ret; work_left = NULL; work_right = NULL; work_out = NULL; ret = NULL; // check argument if (!PyArg_ParseTuple(args, "cOO", &operator, &left_term, &right_term)) { PyErr_SetString(PyExc_TypeError, "Invalid argument"); goto EXIT_WRAPPER_CALC_ARRAY; } // check object type if (!PyList_Check(left_term) || !PyList_Check(right_term)) { PyErr_SetString(PyExc_TypeError, "Need to list object"); goto EXIT_WRAPPER_CALC_ARRAY; } // get list length size = (int32_t)PyList_Size(left_term); // check list length if (size != (int32_t)PyList_Size(right_term)) { PyErr_SetString(PyExc_RuntimeError, "Size of list does not mismatch"); goto EXIT_WRAPPER_CALC_ARRAY; } // malloc memory work_left = (double *)malloc(sizeof(double) * size); work_right = (double *)malloc(sizeof(double) * size); work_out = (double *)malloc(sizeof(double) * size); ret = PyList_New(size); // check memory if ((NULL == work_left) || (NULL == work_right) || (NULL == work_out) || (NULL == ret)) { PyErr_SetString(PyExc_MemoryError, "lack of memory"); Py_XDECREF(ret); // consider ret is NULL ret = NULL; goto EXIT_WRAPPER_CALC_ARRAY; } // copy data for (idx = 0; idx < size; idx++) { // リストから取り出したPyObject型をdouble型に変換し，配列に格納 work_left[idx] = PyFloat_AsDouble(PyList_GetItem(left_term, idx)); work_right[idx] = PyFloat_AsDouble(PyList_GetItem(right_term, idx)); } // calculate return_code = calc_array(size, operator, (const double *)work_left, (const double *)work_right, work_out); // check return code if (return_code == 0) { // copy result for (idx = 0; idx < size; idx++) { // double型をPyObject型に変換し，リストの該当箇所に格納 PyList_SetItem(ret, idx, PyFloat_FromDouble(work_out[idx])); } } else { PyErr_SetString(PyExc_RuntimeError, "Calculation failed"); Py_DECREF(ret); // 失敗した場合は，確保したリストを削除 ret = NULL; goto EXIT_WRAPPER_CALC_ARRAY; } EXIT_WRAPPER_CALC_ARRAY: if (NULL != work_left) { free(work_left); } if (NULL != work_right) { free(work_right); } if (NULL != work_out) { free(work_out); } return ret; } // ここまで static PyMethodDef custom_methods[] = { {"add", wrapper_add, METH_VARARGS, NULL}, {"set_value", wrapper_set_value, METH_VARARGS, NULL}, {"newton", wrapper_newton_method, METH_VARARGS, NULL}, // 追加部分2 {"calc_array", wrapper_calc_array, METH_VARARGS, NULL}, // ここまで {NULL, NULL, 0, NULL} }; static struct PyModuleDef custommodule = { PyModuleDef_HEAD_INIT, "custommodule", "", -1, custom_methods, }; PyMODINIT_FUNC PyInit_custommodule(void) { return PyModule_Create(&custommodule); }
コンパイル
前回のShell Scriptと同一のため，割愛
動作確認
こちらも，前回の結果に加える形で実装した．
import custommodule as c_mod # add function uses static variable # initial value of static variable is 0 c = c_mod.add(2, 3) print('c_mod.add(2, 3) = ', c) # 2 + 3 + 0 -> 5 c_mod.set_value(1) # set 1 to static variable print('c_mod.set_value(1)') c = c_mod.add(2, 3) print('c_mod.add(2, 3) = ', c) # 2 + 3 + 1 -> 6 # newton function uses function pointer f = lambda x: x * x - 2.0 # define function est_x = c_mod.newton(2.0, 10, f) print('c_mod.newton(2.0, 10, f) = ', est_x) # sqrt(2.0) -> 1.4142135... # 追加部分 xs = [0.5, 2.1, 3.2] ys = [0.5, 1.1, -3.2] zs = c_mod.calc_array(b'+', xs, ys) convert_f = lambda xs: ', '.join([str(val) for val in xs]) print("c_mod.calc_array(b'+', [{}], [{}]) = ".format(convert_f(xs), convert_f(ys)), zs) # ================== # exception examples # ================== # Invalid argument try: c_mod.calc_array('+', xs, ys) except Exception as e: print(e) # Need to list object try: c_mod.calc_array(b'+', tuple(xs), ys) except Exception as e: print(e) # Size of list does not mismatch try: c_mod.calc_array(b'+', xs, ys + [1.1]) except Exception as e: print(e) # Calculation failed try: c_mod.calc_array(b'/', xs, ys) except Exception as e: print(e) # ここまで
c_mod.add(2, 3) = 5 c_mod.set_value(1) c_mod.add(2, 3) = 6 c_mod.newton(2.0, 10, f) = 1.414213562373095 # 追加部分 c_mod.calc_array(b'+', [0.5, 2.1, 3.2], [0.5, 1.1, -3.2]) = [1.0, 3.2, 0.0] Invalid argument Need to list object Size of list does not mismatch Calculation failed # ここまで
期待通りの結果が得られている．
気になる点
動作はしたが，以下の2点が気になる．
- 演算時，一時的にメモリ使用量が2倍以上になる．この対策はないのか．
- Py_DECREFを利用して確保した領域を解放しているつもりだが，期待通りの動作をしているか．
