Cython：class 和 cdef class，使用 C++¶

class 和 cdef class¶

class 定义属性变量比较自由，cdef class 可以定义 cdef

class 使用 init 初始化，cdef class 在使用 init 之前用 cinit 对 C 相关的参数进行初始化。

cdef class 中的方法可以是 def, cdef, cpdef 三种，只有 public 的属性才可以被访问，不可以添加新的属性。

dealloc 函数类似析构函数，负责释放申请的内存。

Cython 属性可以使用关键词 property 来定义，然后定义 get 和 set 方法来进行获取和设置：

  1. property name:
  2.     def __get__(self):
  3.         return something
  4.     def __set__(self):
  5.         set_something

使用 C++ 类¶

使用 C++ 类时要加上 cppclass 关键词，在编译时 setup 中要加上 language="c++" 的选项。

假设我们有这样一个 C++ 类：

In [1]:

  1. %%file particle_extern.h
  2. #ifndef _PARTICLE_EXTERN_H_
  3. #define _PARTICLE_EXTERN_H_
  4.  
  5. class Particle {
  6.  
  7.     public:
  8.  
  9.         Particle() :
  10.             mass(0), charge(0) {}
  11.  
  12.         Particle(float m, float c, float *p, float *v);
  13.  
  14.         ~Particle() {}
  15.  
  16.         float getMass() {return mass; }
  17.  
  18.         void setMass(float m) { mass = m; }
  19.  
  20.         float getCharge() { return charge; }
  21.  
  22.         const float *getVel() { return vel; }
  23.         const float *getPos() { return pos; }
  24.  
  25.         void applyImpulse(float *f, float t);
  26.  
  27.     private:
  28.         float mass, charge;
  29.         float pos[3], vel[3];
  30. };
  31.  
  32. #endif
  1. Overwriting particle_extern.h

In [2]:

  1. %%file particle_extern.cpp
  2. #include "particle_extern.h"
  3.  
  4. Particle::Particle(float m, float c, float *p, float *v) :
  5.     mass(m), charge(c) 
  6. {
  7.     for (int i=0; i<3; ++i) {
  8.         pos[i] = p[i]; vel[i] = v[i];
  9.     }
  10. }
  11.  
  12. void Particle::applyImpulse(float *f, float t)
  13. {
  14.     float newvi;
  15.     for(int i=0; i<3; ++i) {
  16.         newvi = vel[i] + t / mass * f[i];
  17.         pos[i] = (newvi + vel[i]) * t / 2.;
  18.         vel[i] = newvi;
  19.     }
  20. }
  1. Overwriting particle_extern.cpp

在 Cython 中调用这个类：

In [3]:

  1. %%file particle.pyx
  2. import numpy as np
  3.  
  4. cdef extern from "particle_extern.h":
  5.  
  6.     cppclass _Particle "Particle":
  7.         _Particle(float m, float c, float *p, float *v)
  8.         float getMass()
  9.         void setMass(float m)
  10.         float getCharge()
  11.         const float *getVel()
  12.         const float *getPos()
  13.         void applyImpulse(float *f, float t)
  14.  
  15.  
  16. cdef class Particle:
  17.     cdef _Particle *thisptr # ptr to C++ instance
  18.  
  19.     def __cinit__(self, m, c, float[::1] p, float[::1] v):
  20.         if p.shape[0] != 3 or v.shape[0] != 3:
  21.             raise ValueError("...")
  22.         self.thisptr = new _Particle(m, c, &p[0], &v[0])
  23.  
  24.     def __dealloc__(self):
  25.         del self.thisptr
  26.  
  27.     def apply_impulse(self, float[::1] v, float t):
  28.         self.thisptr.applyImpulse(&v[0], t)
  29.  
  30.     def __repr__(self):
  31.         args = ', '.join('%s=%s' % (n, getattr(self, n)) for n in ('mass', 'charge', 'pos', 'vel'))
  32.         return 'particle.Particle(%s)' % args
  33.  
  34.     property charge:
  35.  
  36.         def __get__(self):
  37.             return self.thisptr.getCharge()
  38.  
  39.     property mass:  # Cython-style properties.
  40.         def __get__(self):
  41.             return self.thisptr.getMass()
  42.  
  43.         def __set__(self, m):
  44.             self.thisptr.setMass(m)
  45.  
  46.     property vel:
  47.  
  48.         def __get__(self):
  49.             cdef const float *_vel = self.thisptr.getVel()
  50.             cdef float[::1] arr = np.empty((3,), dtype=np.float32)
  51.             for i in range(3):
  52.                 arr[i] = _vel[i]
  53.             return np.asarray(arr)
  54.  
  55.     property pos:
  56.  
  57.         def __get__(self):
  58.             cdef const float *_pos = self.thisptr.getPos()
  59.             cdef float[::1] arr = np.empty((3,), dtype=np.float32)
  60.             for i in range(3):
  61.                 arr[i] = _pos[i]
  62.             return np.asarray(arr)
  1. Overwriting particle.pyx

首先从头文件声明这个类：

  1. cdef extern from "particle_extern.h":
  2.  
  3.     cppclass _Particle "Particle":
  4.         _Particle(float m, float c, float *p, float *v)
  5.         float getMass()
  6.         void setMass(float m)
  7.         float getCharge()
  8.         const float *getVel()
  9.         const float *getPos()
  10.         void applyImpulse(float *f, float t)

这里要使用 cppclass 关键词，并且为了方便，我们将 Particle 类的名字在 Cython 中重命名为 _Particle。

  1. cdef class Particle:
  2.     cdef _Particle *thisptr
  3.     def __cinit__(self, m, c, float[::1] p, float[::1] v):
  4.         if p.shape[0] != 3 or v.shape[0] != 3:
  5.             raise ValueError("...")
  6.         self.thisptr = new _Particle(m, c, &p[0], &v[0])

为了使用这个类，我们需要定义一个该类的指针，然后用指针指向一个 _Particle 对象。

In [4]:

  1. %%file setup.py
  2. from distutils.core import setup
  3. from distutils.extension import Extension
  4. from Cython.Distutils import build_ext
  5.  
  6. ext = Extension("particle", ["particle.pyx", "particle_extern.cpp"], language="c++")
  7.  
  8. setup(
  9.     cmdclass = {'build_ext': build_ext},
  10.     ext_modules = [ext],
  11. )
  1. Overwriting setup.py

要加上 language="c++" 的选项，然后编译：

In [5]:

  1. !python setup.py build_ext -i
  1. running build_ext
  2. cythoning particle.pyx to particle.cpp
  3. building 'particle' extension
  4. C:\Anaconda\Scripts\gcc.bat -DMS_WIN64 -mdll -O -Wall -IC:\Anaconda\include -IC:\Anaconda\PC -c particle.cpp -o build\temp.win-amd64-2.7\Release\particle.o
  5. C:\Anaconda\Scripts\gcc.bat -DMS_WIN64 -mdll -O -Wall -IC:\Anaconda\include -IC:\Anaconda\PC -c particle_extern.cpp -o build\temp.win-amd64-2.7\Release\particle_extern.o
  6. writing build\temp.win-amd64-2.7\Release\particle.def
  7. C:\Anaconda\Scripts\g++.bat -DMS_WIN64 -shared -s build\temp.win-amd64-2.7\Release\particle.o build\temp.win-amd64-2.7\Release\particle_extern.o build\temp.win-amd64-2.7\Release\particle.def -LC:\Anaconda\libs -LC:\Anaconda\PCbuild\amd64 -lpython27 -lmsvcr90 -o "C:\Users\lijin\Documents\Git\python-tutorial\07. interfacing with other languages\particle.pyd"
  1. particle.cpp: In function 'void __Pyx_RaiseArgtupleInvalid(const char*, int, Py_ssize_t, Py_ssize_t, Py_ssize_t)':
  2. particle.cpp:14931:59: warning: unknown conversion type character 'z' in format [-Wformat]
  3. particle.cpp:14931:59: warning: format '%s' expects argument of type 'char*', but argument 5 has type 'Py_ssize_t {aka long long int}' [-Wformat]
  4. particle.cpp:14931:59: warning: unknown conversion type character 'z' in format [-Wformat]
  5. particle.cpp:14931:59: warning: too many arguments for format [-Wformat-extra-args]
  6. particle.cpp: In function 'int __Pyx_BufFmt_ProcessTypeChunk(__Pyx_BufFmt_Context*)':
  7. particle.cpp:15498:78: warning: unknown conversion type character 'z' in format [-Wformat]
  8. particle.cpp:15498:78: warning: unknown conversion type character 'z' in format [-Wformat]
  9. particle.cpp:15498:78: warning: too many arguments for format [-Wformat-extra-args]
  10. particle.cpp:15550:67: warning: unknown conversion type character 'z' in format [-Wformat]
  11. particle.cpp:15550:67: warning: unknown conversion type character 'z' in format [-Wformat]
  12. particle.cpp:15550:67: warning: too many arguments for format [-Wformat-extra-args]
  13. particle.cpp: In function 'PyObject* __pyx_buffmt_parse_array(__Pyx_BufFmt_Context*, const char**)':
  14. particle.cpp:15612:69: warning: unknown conversion type character 'z' in format [-Wformat]
  15. particle.cpp:15612:69: warning: format '%d' expects argument of type 'int', but argument 3 has type 'size_t {aka long long unsigned int}' [-Wformat]
  16. particle.cpp:15612:69: warning: too many arguments for format [-Wformat-extra-args]
  17. particle.cpp: In function 'int __Pyx_GetBufferAndValidate(Py_buffer*, PyObject*, __Pyx_TypeInfo*, int, int, int, __Pyx_BufFmt_StackElem*)':
  18. particle.cpp:15797:73: warning: unknown conversion type character 'z' in format [-Wformat]
  19. particle.cpp:15797:73: warning: format '%s' expects argument of type 'char*', but argument 3 has type 'Py_ssize_t {aka long long int}' [-Wformat]
  20. particle.cpp:15797:73: warning: unknown conversion type character 'z' in format [-Wformat]
  21. particle.cpp:15797:73: warning: too many arguments for format [-Wformat-extra-args]
  22. particle.cpp: In function 'void __Pyx_RaiseTooManyValuesError(Py_ssize_t)':
  23. particle.cpp:16216:94: warning: unknown conversion type character 'z' in format [-Wformat]
  24. particle.cpp:16216:94: warning: too many arguments for format [-Wformat-extra-args]
  25. particle.cpp: In function 'void __Pyx_RaiseNeedMoreValuesError(Py_ssize_t)':
  26. particle.cpp:16222:48: warning: unknown conversion type character 'z' in format [-Wformat]
  27. particle.cpp:16222:48: warning: format '%s' expects argument of type 'char*', but argument 3 has type 'Py_ssize_t {aka long long int}' [-Wformat]
  28. particle.cpp:16222:48: warning: too many arguments for format [-Wformat-extra-args]
  29. particle.cpp: In function 'int __Pyx_ValidateAndInit_memviewslice(int*, int, int, int, __Pyx_TypeInfo*, __Pyx_BufFmt_StackElem*, __Pyx_memviewslice*, PyObject*)':
  30. particle.cpp:16941:50: warning: unknown conversion type character 'z' in format [-Wformat]
  31. particle.cpp:16941:50: warning: format '%s' expects argument of type 'char*', but argument 3 has type 'Py_ssize_t {aka long long int}' [-Wformat]
  32. particle.cpp:16941:50: warning: unknown conversion type character 'z' in format [-Wformat]
  33. particle.cpp:16941:50: warning: too many arguments for format [-Wformat-extra-args]

In [6]:

  1. import particle

注意这里类型要设成 float32，因为 C++ 程序中接受的是 float 类型，默认是 float64(double) 类型：

In [7]:

  1. import numpy as np
  2.  
  3. pos = vel = np.arange(3., dtype='float32')
  4. mass = 1.0
  5. charge = 2.0
  6.  
  7. p = particle.Particle(mass, charge, pos, vel)
  8. p

Out[7]:

  1. particle.Particle(mass=1.0, charge=2.0, pos=[ 0.  1.  2.], vel=[ 0.  1.  2.])

调用 apply_impulse 方法：

In [8]:

  1. p.apply_impulse(np.arange(3., dtype='float32'), 1.0)
  2.  
  3. p

Out[8]:

  1. particle.Particle(mass=1.0, charge=2.0, pos=[ 0.   1.5  3. ], vel=[ 0.  2.  4.])

查看质量：

In [9]:

  1. p.mass

Out[9]:

  1. 1.0

修改质量：

In [10]:

  1. p.mass = 3.0

查看 charge：

In [11]:

  1. p.charge

Out[11]:

  1. 2.0

因为 charge 没有定义 set 方法，所以它是只读的属性，不能进行修改。

In [12]:

  1. import zipfile
  2.  
  3. f = zipfile.ZipFile('07-05-particle.zip','w',zipfile.ZIP_DEFLATED)
  4.  
  5. names = ['particle.pyx',
  6.          'particle_extern.cpp',
  7.          'particle_extern.h',
  8.          'setup.py']
  9. for name in names:
  10.     f.write(name)
  11.  
  12. f.close()
  13.  
  14. !rm -f setup*.*
  15. !rm -f particle*.*
  16. !rm -rf build

原文: https://nbviewer.jupyter.org/github/lijin-THU/notes-python/blob/master/07-interfacing-with-other-languages/07.05-cython-part-3.ipynb