Analysis on C ++ calling Python Module

Analysis on C ++ calling Python Module
Analysis on C ++ calling Python Module

As a glue language,PythonEasy to callC,C ++Can also be called in other languages.PythonModule.

PythonProvidedC ++Library, so that developers can easilyC ++Program callPythonModule.

For specific documents, refer to the official guide:
Embedding Python in Another Application

Call method 1 Link PythonCall Library

PythonThe installation directory contains the header file (includeDirectory) and library files (WindowsWhich ispython27.lib).

You need to link to this library before using it.

2. Direct call PythonStatement

# Include "python/Python. h" int main () {Py_Initialize (); # initialize PyRun_SimpleString ("print 'hello'"); Py_Finalize (); # release resources}

3 load PythonModule and call Functions

~/testDirectory containstest.py:

def test_add(a, b):    print 'add ', a, ' and ', b    return a+b

You can use the following code to calltest_addFunction:

# Include "python/Python. h" # include
  
   
Using namespace std; int main () {Py_Initialize (); // initialize // switch the Python working path to the directory where the module to be called is located. Ensure that the path name is correct. string path = "~ /Test "; string chdir_cmd = string (" sys. path. append (\ "") + path + "\") "; const char * cstr_cmd = chdir_1_.c_str (); PyRun_SimpleString (" import sys "); PyRun_SimpleString (cstr_cmd ); // load the module PyObject * moduleName = PyString_FromString ("test"); // The Module name, not the file name PyObject * pModule = PyImport_Import (moduleName); if (! PModule) // failed to load the module {cout <"[ERROR] Python get module failed. "<endl; return 0 ;}cout <" [INFO] Python get module succeed. "<endl; // load function PyObject * pv = PyObject_GetAttrString (pModule," test_add "); if (! Pv |! PyCallable_Check (pv) // verify whether the load is successful {cout <"[ERROR] Can't find funftion (test_add)" <endl; return 0 ;} cout <"[INFO] Get function (test_add) succeed. "<endl; // set the PyObject * args = PyTuple_New (2); // two parameters: PyObject * arg1 = PyInt_FromLong (4 ); // set parameter 1 to 4 PyObject * arg2 = PyInt_FromLong (3); // set parameter 2 to 3 PyTuple_SetItem (args, 0, arg1); PyTuple_SetItem (args, 1, arg2); // call the function PyObject * pRet = PyObject_CallObject (pv, args); // obtain the parameter if (pRet) // verify whether the call is successful {long result = PyInt_AsLong (pRet); cout <"result:" <result;} Py_Finalize () ;## release resource return 0 ;}
  

Parameter transfer 1 C ++Direction PythonPASS Parameters

PythonThe parameter is actually a tuple, so passing the parameter is actually constructing a suitable tuple.

There are two common methods:

UsePyTuple_NewCreate tuples,PyTuple_SetItemSet the tuples

PyObject * args = PyTuple_New (3); PyObject * arg1 = Py_BuildValue ("I", 100); // The integer parameter PyObject * arg2 = Py_BuildValue ("f", 3.14 ); // Floating Point Number Parameter PyObject * arg3 = Py_BuildValue ("s", "hello"); // string parameter PyTuple_SetItem (args, 0, arg1); PyTuple_SetItem (args, 1, arg2); PyTuple_SetItem (args, 2, arg3 );

Directly use Py_BuildValue to construct the tuples

PyObject * args = Py_BuildValue ("ifs", 100, 3.14, "hello"); PyObject * args = Py_BuildValue ("()"); // No Parameter Function

i,s,fFor more information about format strings, see format strings.

2 Conversion PythonReturn Value

CallPythonAll obtained are PyObject objects, so you need to usePythonSome functions in the provided library convert the return valueC ++For examplePyInt_AsLong,PyFloat_AsDouble,PyString_AsString.

You can also usePyArg_ParseTupleFunction to parse the returned values as tuples.

PyArg_ParseIt is also a convenient conversion function.

PyArg_ParseTupleAndPyArg_ParseBoth use format strings

Note: PythonTo switch to the module path, load the module by the module name instead of the file name module, or verify whether the function is loaded successfully. Otherwise, a stack error may occur, causing program crash. Py_DECREF(PyObject*)To remove object references (for Python garbage collection)