通過C API從字符串創建並調用python函數

Question

是否可以從字符串加載python函數，然後使用參數調用該函數並獲取返回值？

我正在使用python C API從我的C++應用程序中運行python代碼。我可以使用PyImport_Import從文件加載模塊，使用PyObject_GetAttrString從中獲取函數對象，然後使用PyObject_CallObject調用該函數。我想要做的是從字符串而不是文件加載模塊/函數。是否有一些相當於PyImport_Import這將允許我傳遞一個字符串而不是文件？我需要傳遞參數給我打電話的函數，我需要訪問返回值，所以我不能只使用PyRun_SimpleString。

---

編輯：

我發現剛剛開始瞭解PyRun_String後，這一解決方案。我正在創建一個新模塊，獲取其字典對象，並在調用PyRun_String時將其傳遞給我的新模塊中的一個函數，然後爲該新創建的函數獲取一個函數對象，並通過PyObject_CallObject調用它，傳遞我的參數。這是我找到了解決我的問題： main.cpp

int main() 
{ 
    PyObject *pName, *pModule, *pArgs, *pValue, *pFunc; 
    PyObject *pGlobal = PyDict_New(); 
    PyObject *pLocal; 

    //Create a new module object 
    PyObject *pNewMod = PyModule_New("mymod"); 

    Py_Initialize(); 
    PyModule_AddStringConstant(pNewMod, "__file__", ""); 

    //Get the dictionary object from my module so I can pass this to PyRun_String 
    pLocal = PyModule_GetDict(pNewMod); 

    //Define my function in the newly created module 
    pValue = PyRun_String("def blah(x):\n\tprint 5 * x\n\treturn 77\n", Py_file_input, pGlobal, pLocal); 
    Py_DECREF(pValue); 

    //Get a pointer to the function I just defined 
    pFunc = PyObject_GetAttrString(pNewMod, "blah"); 

    //Build a tuple to hold my arguments (just the number 4 in this case) 
    pArgs = PyTuple_New(1); 
    pValue = PyInt_FromLong(4); 
    PyTuple_SetItem(pArgs, 0, pValue); 

    //Call my function, passing it the number four 
    pValue = PyObject_CallObject(pFunc, pArgs); 
    Py_DECREF(pArgs); 
    printf("Returned val: %ld\n", PyInt_AsLong(pValue)); 
    Py_DECREF(pValue); 

    Py_XDECREF(pFunc); 
    Py_DECREF(pNewMod); 
    Py_Finalize(); 

    return 0; 
} 

---

這是我原來的職位的休息，爲後人留下了：

這裏就是我最初做： main.cpp ：

#include <Python.h> 

int main() 
{ 
    PyObject *pName, *pModule, *pArgs, *pValue, *pFunc; 

    Py_Initialize(); 
    PyRun_SimpleString("import sys"); 
    PyRun_SimpleString("sys.path.append('')"); 
    pName = PyString_FromString("atest"); 
    pModule = PyImport_Import(pName); 
    Py_DECREF(pName); 

    if(pModule == NULL) 
    { 
     printf("PMod is null\n"); 
     PyErr_Print(); 
     return 1; 
    } 

    pFunc = PyObject_GetAttrString(pModule, "doStuff"); 
    pArgs = PyTuple_New(1); 
    pValue = PyInt_FromLong(4); 
    PyTuple_SetItem(pArgs, 0, pValue); 

    pValue = PyObject_CallObject(pFunc, pArgs); 
    Py_DECREF(pArgs); 
    printf("Returned val: %ld\n", PyInt_AsLong(pValue)); 
    Py_DECREF(pValue); 

    Py_XDECREF(pFunc); 
    Py_DECREF(pModule); 

    Py_Finalize(); 

    return 0; 
} 

而且atest.py：

def doStuff(x): 
    print "X is %d\n" % x 
    return 2 * x 

Answer 1

PyRun_String在Python C API中可能是你正在尋找的東西。見：http://docs.python.org/c-api/veryhigh.html

Answer 2

問題中包含的答案很好，但我有一些小的麻煩，使用它與Python 3.5，所以爲了節省任何人做我做的，下面是一個稍微編輯的版本，似乎這個版本工作得很好的Python至少：

#include <Python.h> 

int main(void) 
{ 
    PyObject *pArgs, *pValue, *pFunc, *pModule, *pGlobal, *pLocal; 

    Py_Initialize(); 

    pGlobal = PyDict_New(); 

    //Create a new module object 
    pModule = PyModule_New("mymod"); 
    PyModule_AddStringConstant(pModule, "__file__", ""); 

    //Get the dictionary object from my module so I can pass this to PyRun_String 
    pLocal = PyModule_GetDict(pModule); 

    //Define my function in the newly created module 
    pValue = PyRun_String("def blah(x):\n\ty = x * 5\n\treturn y\n", 
     Py_file_input, pGlobal, pLocal); 

    //pValue would be null if the Python syntax is wrong, for example 
    if (pValue == NULL) { 
     if (PyErr_Occurred()) { 
      PyErr_Print(); 
     } 
     return 1; 
    } 

    //pValue is the result of the executing code, 
    //chuck it away because we've only declared a function 
    Py_DECREF(pValue); 

    //Get a pointer to the function I just defined 
    pFunc = PyObject_GetAttrString(pModule, "blah"); 

    //Double check we have actually found it and it is callable 
    if (!pFunc || !PyCallable_Check(pFunc)) { 
     if (PyErr_Occurred()) { 
      PyErr_Print(); 
     } 
     fprintf(stderr, "Cannot find function \"blah\"\n"); 
     return 2; 
    } 

    //Build a tuple to hold my arguments (just the number 4 in this case) 
    pArgs = PyTuple_New(1); 
    pValue = PyLong_FromLong(4); 
    PyTuple_SetItem(pArgs, 0, pValue); 

    //Call my function, passing it the number four 
    pValue = PyObject_CallObject(pFunc, pArgs); 

    fprintf(stdout, "Returned value: %ld\n", PyLong_AsLong(pValue)); 

    Py_DECREF(pValue); 
    Py_XDECREF(pFunc); 

    Py_Finalize(); 

    return 0; 
}