[C++/Python] 如何在C++中使用一个Python类? (Use Python-defined class in C++)
最近在做基于OpenCV的车牌识别, 其中需要用到深度学习的一些代码(Python), 所以一开始的时候开发语言选择了Python(祸患之源).
固然现在Python的速度不算太慢, 但你一定要用Python来操作图像, 实现某些算法的时候, 效率就变得非常重要. 可惜的是, Python在大多数算法实现中, 由于其循环操作实在是太慢, 导致实现的算法效率非常之低.
所以现在我要把深度学习中的一个类(分类器)转换到C++中, 在这个过程之前, 需要做一些test projects, 我主要参照的文章是: C++调用Python(3).
开发环境为 VS2012, WIN7 64.
所有代码都在最后放出, 这里先逐步讲解.
首先我们需要导入合适的头文件: Python.h, 它位于你的Python安装目录的include目录下. (2.6, 2.7版本实测通过)
使用VS的话, 可以按如下方法设置一下项目属性:
- 调试 -> xxx属性(最后一栏) -> VC++目录 -> 右侧库目录
- 增加C:\Python27\libs, 具体路径个人可能不同.
这样就完成了最基本的配置, 下面我们开始导入.py文件并使用它.
我们使用的.py文件非常简单, 代码如下:
1 #!/usr/bin/python
2 # Filename: testpy.py
3 class Person: 4 def sayHi(self): 5 print 'hi'
6 class Second: 7 def invoke(self,obj): 8 obj.sayHi() 9 def sayhi(name): 10 print 'hi',name;
注: 下述所有导入方法在导入失败时不会报错, 只会返回空指针.
第一步是导入.py文件:
- 使用PyObject* pModule来存储导入的.py文件模块, 调用的方法是PyImport_ImportModule(path): PyObject* pModule = PyImport_ImportModule("testpy");
- 使用PyObject* pDict来存储导入模块中的方法字典, 调用的方法是PyModule_GetDict(module): PyObject* pDict = PyModule_GetDict(pModule);
这样就完成了.py文件的导入.
第二步是导入已导入模块中的方法或类:
- 获取方法, 调用的方法是PyDict_GetItemString(dict, methodName): PyObject* pFunHi = PyDict_GetItemString(pDict, "sayhi");
- 获取类, 调用的方法同上, 注意红体部分的字符串对应于.py文件中的类/方法名: PyObject* pClassSecond = PyDict_GetItemString(pDict, "Second");
第三步是使用导入的方法或类:
- 使用方法, 调用PyObject_CallFunction(pFunc, "s", args)即可: PyObject_CallFunction(pFunHi, "s", "lhb");
- 使用类构造对象, 调用PyInstance_New(pClass, NULL, NULL)即可: PyObject* pInstanceSecond = PyInstance_New(pClassSecond, NULL, NULL); , 注意其中的pClassSecond为第二步.2中获取的类指针
- 使用类对象的方法, 调用PyObject_CallMethod(pInstance, methodname, "O", args)即可: PyObject_CallMethod(pInstanceSecond, "invoke", "O", pInstancePerson);
- 上述调用中的"s"和"O"代表的是参数列表的类型, 我们可以在 Py_BuildValue 找到所有的类型, 本文最后也附了此表.
最后不要忘记销毁这些对象: Py_DECREF(pointer);
下面是C++的实现代码, 代码来自于我参考的博客, 略有修改.
1 /*
2 * test.cpp 3 * Created on: 2010-8-12 4 * Author: lihaibo 5 */
6 #include <C:/Python27/include/Python.h>
7 #include <iostream>
8 #include <string>
9
10 int main(void) { 11 Py_Initialize(); // 启动虚拟机
12 if (!Py_IsInitialized()) 13 return -1; 14 // 导入模块
15 PyObject* pModule = PyImport_ImportModule("testpy"); 16 if (!pModule) { 17 printf("Cant open python file!/n"); 18 return -1; 19 } 20 // 模块的字典列表
21 PyObject* pDict = PyModule_GetDict(pModule); 22 if (!pDict) { 23 printf("Cant find dictionary./n"); 24 return -1; 25 } 26 // 演示函数调用
27 PyObject* pFunHi = PyDict_GetItemString(pDict, "sayhi"); 28 PyObject_CallFunction(pFunHi, "s", "lhb"); 29 Py_DECREF(pFunHi); 30 // 演示构造一个Python对象，并调用Class的方法 31 // 获取Second类
32 PyObject* pClassSecond = PyDict_GetItemString(pDict, "Second"); 33 if (!pClassSecond) { 34 printf("Cant find second class./n"); 35 return -1; 36 } 37 //获取Person类
38 PyObject* pClassPerson = PyDict_GetItemString(pDict, "Person"); 39 if (!pClassPerson) { 40 printf("Cant find person class./n"); 41 return -1; 42 } 43 //构造Second的实例
44 PyObject* pInstanceSecond = PyInstance_New(pClassSecond, NULL, NULL); 45 if (!pInstanceSecond) { 46 printf("Cant create second instance./n"); 47 return -1; 48 } 49 //构造Person的实例
50 PyObject* pInstancePerson = PyInstance_New(pClassPerson, NULL, NULL); 51 if (!pInstancePerson) { 52 printf("Cant find person instance./n"); 53 return -1; 54 } 55 //把person实例传入second的invoke方法
56 PyObject_CallMethod(pInstanceSecond, "invoke", "O", pInstancePerson); 57 //释放
58 Py_DECREF(pInstanceSecond); 59 Py_DECREF(pInstancePerson); 60 Py_DECREF(pClassSecond); 61 Py_DECREF(pClassPerson); 62 Py_DECREF(pModule); 63 Py_Finalize(); // 关闭虚拟机
64 return 0; 65 }
类型参照:
- s (string) [char *]
- Convert a null-terminated C string to a Python object. If the C string pointer is NULL, None is used.
- s# (string) [char *, int]
- Convert a C string and its length to a Python object. If the C string pointer is NULL, the length is ignored and None is returned.
- z (string or None) [char *]
- Same as s.
- z# (string or None) [char *, int]
- Same as s#.
- u (Unicode string) [Py_UNICODE *]
- Convert a null-terminated buffer of Unicode (UCS-2 or UCS-4) data to a Python Unicode object. If the Unicode buffer pointer is NULL, Noneis returned.
- u# (Unicode string) [Py_UNICODE *, int]
- Convert a Unicode (UCS-2 or UCS-4) data buffer and its length to a Python Unicode object. If the Unicode buffer pointer is NULL, the length is ignored and None is returned.
- i (integer) [int]
- Convert a plain C int to a Python integer object.
- b (integer) [char]
- Convert a plain C char to a Python integer object.
- h (integer) [short int]
- Convert a plain C short int to a Python integer object.
- l (integer) [long int]
- Convert a C long int to a Python integer object.
- B (integer) [unsigned char]
- Convert a C unsigned char to a Python integer object.
- H (integer) [unsigned short int]
- Convert a C unsigned short int to a Python integer object.
- I (integer/long) [unsigned int]
- Convert a C unsigned int to a Python integer object or a Python long integer object, if it is larger than sys.maxint.
- k (integer/long) [unsigned long]
- Convert a C unsigned long to a Python integer object or a Python long integer object, if it is larger than sys.maxint.
- L (long) [PY_LONG_LONG]
- Convert a C long long to a Python long integer object. Only available on platforms that support long long.
- K (long) [unsigned PY_LONG_LONG]
- Convert a C unsigned long long to a Python long integer object. Only available on platforms that support unsigned long long.
- n (int) [Py_ssize_t]
-
Convert a C Py_ssize_t to a Python integer or long integer.
New in version 2.5.
- c (string of length 1) [char]
- Convert a C int representing a character to a Python string of length 1.
- d (float) [double]
- Convert a C double to a Python floating point number.
- f (float) [float]
- Same as d.
- D (complex) [Py_complex *]
- Convert a C Py_complex structure to a Python complex number.
- O (object) [PyObject *]
- Pass a Python object untouched (except for its reference count, which is incremented by one). If the object passed in is a NULL pointer, it is assumed that this was caused because the call producing the argument found an error and set an exception. Therefore, Py_BuildValue()will return NULL but won’t raise an exception. If no exception has been raised yet, SystemError is set.
- S (object) [PyObject *]
- Same as O.
- N (object) [PyObject *]
- Same as O, except it doesn’t increment the reference count on the object. Useful when the object is created by a call to an object constructor in the argument list.
- O& (object) [converter, anything]
- Convert anything to a Python object through a converter function. The function is called with anything (which should be compatible withvoid *) as its argument and should return a “new” Python object, or NULL if an error occurred.
- (items) (tuple) [matching-items]
- Convert a sequence of C values to a Python tuple with the same number of items.
- [items] (list) [matching-items]
- Convert a sequence of C values to a Python list with the same number of items.
- {items} (dictionary) [matching-items]
- Convert a sequence of C values to a Python dictionary. Each pair of consecutive C values adds one item to the dictionary, serving as key and value, respectively.
If there is an error in the format string, the SystemError exception is set and NULL returned.