C ++ calls the basic functions of Python and calls the basic functions of python.

C ++ calls the basic functions of Python and calls the basic functions of python.

C ++ calls Python to install Python first. Taking win7 as an example, the Python path is c: \ Python35 \, and c ++ code is compiled through mingw.
To compile a makefile file, you must first add the inclusion path:
Inc_path + = c:/Python35/include
Then add the link parameters:
Ld_flag + = c:/Python35/libs/libpython35.a
Add header file reference to the source file:
# Include "Python. h"
The Python interpreter must be initialized and terminated after the task is completed:

1 void start () 2 {3 int r = Py_IsInitialized (); // 1 indicates that 4 if (r = 0) has been initialized) 5 {6 // Py_SetPythonHome (L "C :\\ Python35"); 7 Py_Initialize (); // initialize 8 p_main_Module = PyImport_ImportModule ("_ main __"); 9 if (! P_main_Module) 10 {11 throw ""; 12} 13} 14} 15 void end () 16 {17 Py_Finalize (); // clear 18}

During program deployment, you can copy the c: \ Python35 \ lib directory to the execution path, or set the Python installation directory through Py_SetPythonHome (L "C: \ Python35.
Basic Requirements for C ++ to call Python:
1. Run Python commands

PyRun_SimpleString("print(os.getcwd(),a)");pyext.eval(R"(a+='qwer')");

2. Load the Python Module

PyObject * pModule = PyImport_ImportModule ("tp"); // test: Python file name. If the script has an error, null PyRun_SimpleString ("import OS") is returned ");

3. assign values to Python Variables

For numeric values, use Py_BuildValue:

Py_BuildValue("") NonePy_BuildValue("i", 123) 123Py_BuildValue("iii", 123, 456, 789) (123, 456, 789)Py_BuildValue("s", "hello") 'hello'Py_BuildValue("ss", "hello", "world") ('hello', 'world')Py_BuildValue("s#", "hello", 4) 'hell'Py_BuildValue("()") ()Py_BuildValue("(i)", 123) (123,)    Py_BuildValue("(ii)", 123, 456) (123, 456)Py_BuildValue("(i,i)", 123, 456) (123, 456)Py_BuildValue("[i,i]", 123, 456) [123, 456]Py_BuildValue("{s:i,s:i}", "abc", 123, "def", 456) {'abc': 123, 'def': 456}

For other data structures, use the corresponding function settings, for example:

PyObject * pArgs = PyTuple_New (1); PyObject * pDict = PyDict_New (); // create the dictionary type variable PyDict_SetItemString (pDict, "Name", Py_BuildValue ("s ", "WangYao"); // fill in the Data PyDict_SetItemString (pDict, "Age", Py_BuildValue ("I", 25) to the dictionary type variable )); // fill in the Data PyTuple_SetItem (pArgs, 0, pDict) to the dictionary type variable; // 0 --- the serial number adds the dictionary type variable to the parameter tuples

After the object is constructed, set it to Python through PyObject_SetAttrString:

PyObject * ps = PyUnicode_DecodeUTF8 (val, strlen (val), "ignore"); // constructs an object PyObject_SetAttrString (p_main_Module, key, ps); // set

4. Obtain the value of the Python variable.
First, get the pointer of the variable, and then parse it through PyArg_Parse.

PModule = PyImport_ImportModule ("_ main _"); pReturn = PyObject_GetAttrString (pModule, "a"); // you can obtain the global variable int size = PyDict_Size (pReturn ); pyObject * pNewAge = PyDict_GetItemString (pReturn, "Age"); int newAge; PyArg_Parse (pNewAge, "I", & newAge );

Analysis of tuples:

int ok;ok = PyArg_ParseTuple(args, "s", &s); //Python call: f('whoops!')ok = PyArg_ParseTuple(args, "lls", &k, &l, &s);//Python call: f(1, 2,'three')ok = PyArg_ParseTuple(args, "(ii)s#", &i, &j, &s, &size);//Python call: f((1, 2), 'three')ok = PyArg_ParseTuple(args, "s|si", &file, &mode, &bufsize);//Python calls://f('spam')//f('spam', 'w')//f('spam', 'wb', 100000)

5. Call Python Functions

PyObject * pfun = PyObject_GetAttrString (pModule, "testdict"); // testdict: function name in the Python file: PyObject * pReturn = PyEval_CallObject (pfun, pArgs); // call the Function

6. Set the function for Python to call
Define the c function, declare the method list, declare the module, add the module, and call

Static int numargs = 1890; static PyObject * emb_numargs (PyObject * self, PyObject * args) // C function {if (! Callback (args, ": numargs") return NULL; return PyLong_FromLong (numargs);} static PyMethodDef EmbMethods [] = {// method list {"numargs", emb_numargs, METH_VARARGS, "Return the number of arguments already ed by the process. "},{ NULL, NULL, 0, NULL }}; static PyModuleDef EmbModule ={// the module declares PyModuleDef_HEAD_INIT," emb ", NULL,-1, EmbMethods, NULL, NULL, NULL, NULL}; static PyObject * PyInit_emb (void) // module initialization function {return PyModule_Create (& EmbModule);} // Add module: PyImport_AppendInittab ("emb ", & PyInit_emb); // Add the Python code of a module: import embprint ("Number of arguments", emb. numargs ())