07.05 Cython：class 和 cdef class，使用 C++
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：
1property 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：
1%%file particle_extern.h
2#ifndef _PARTICLE_EXTERN_H_
3#define _PARTICLE_EXTERN_H_
4
5class 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
Overwriting particle_extern.h
1%%file particle_extern.cpp
2#include "particle_extern.h"
3
4Particle::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
12void 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}
Overwriting particle_extern.cpp
在 Cython 中调用这个类：
1%%file particle.pyx
2import numpy as np
3
4cdef 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
16cdef 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)
Overwriting particle.pyx
首先从头文件声明这个类：
1cdef 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。
1cdef 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。
1%%file setup.py
2from distutils.core import setup
3from distutils.extension import Extension
4from Cython.Distutils import build_ext
5
6ext = Extension("particle", ["particle.pyx", "particle_extern.cpp"], language="c++")
7
8setup(
9 cmdclass = {'build_ext': build_ext},
10 ext_modules = [ext],
11)
Overwriting setup.py
要加上 language="c++" 的选项，然后编译：
1!python setup.py build_ext -i
running build_ext
cythoning particle.pyx to particle.cpp
building 'particle' extension
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
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
writing build\temp.win-amd64-2.7\Release\particle.def
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"
particle.cpp: In function 'void __Pyx_RaiseArgtupleInvalid(const char*, int, Py_ssize_t, Py_ssize_t, Py_ssize_t)':
particle.cpp:14931:59: warning: unknown conversion type character 'z' in format [-Wformat]
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]
particle.cpp:14931:59: warning: unknown conversion type character 'z' in format [-Wformat]
particle.cpp:14931:59: warning: too many arguments for format [-Wformat-extra-args]
particle.cpp: In function 'int __Pyx_BufFmt_ProcessTypeChunk(__Pyx_BufFmt_Context*)':
particle.cpp:15498:78: warning: unknown conversion type character 'z' in format [-Wformat]
particle.cpp:15498:78: warning: unknown conversion type character 'z' in format [-Wformat]
particle.cpp:15498:78: warning: too many arguments for format [-Wformat-extra-args]
particle.cpp:15550:67: warning: unknown conversion type character 'z' in format [-Wformat]
particle.cpp:15550:67: warning: unknown conversion type character 'z' in format [-Wformat]
particle.cpp:15550:67: warning: too many arguments for format [-Wformat-extra-args]
particle.cpp: In function 'PyObject* __pyx_buffmt_parse_array(__Pyx_BufFmt_Context*, const char**)':
particle.cpp:15612:69: warning: unknown conversion type character 'z' in format [-Wformat]
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]
particle.cpp:15612:69: warning: too many arguments for format [-Wformat-extra-args]
particle.cpp: In function 'int __Pyx_GetBufferAndValidate(Py_buffer*, PyObject*, __Pyx_TypeInfo*, int, int, int, __Pyx_BufFmt_StackElem*)':
particle.cpp:15797:73: warning: unknown conversion type character 'z' in format [-Wformat]
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]
particle.cpp:15797:73: warning: unknown conversion type character 'z' in format [-Wformat]
particle.cpp:15797:73: warning: too many arguments for format [-Wformat-extra-args]
particle.cpp: In function 'void __Pyx_RaiseTooManyValuesError(Py_ssize_t)':
particle.cpp:16216:94: warning: unknown conversion type character 'z' in format [-Wformat]
particle.cpp:16216:94: warning: too many arguments for format [-Wformat-extra-args]
particle.cpp: In function 'void __Pyx_RaiseNeedMoreValuesError(Py_ssize_t)':
particle.cpp:16222:48: warning: unknown conversion type character 'z' in format [-Wformat]
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]
particle.cpp:16222:48: warning: too many arguments for format [-Wformat-extra-args]
particle.cpp: In function 'int __Pyx_ValidateAndInit_memviewslice(int*, int, int, int, __Pyx_TypeInfo*, __Pyx_BufFmt_StackElem*, __Pyx_memviewslice*, PyObject*)':
particle.cpp:16941:50: warning: unknown conversion type character 'z' in format [-Wformat]
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]
particle.cpp:16941:50: warning: unknown conversion type character 'z' in format [-Wformat]
particle.cpp:16941:50: warning: too many arguments for format [-Wformat-extra-args]
1import 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：
1import numpy as np
2
3pos = vel = np.arange(3., dtype='float32')
4mass = 1.0
5charge = 2.0
6
7p = particle.Particle(mass, charge, pos, vel)
8p
particle.Particle(mass=1.0, charge=2.0, pos=[ 0. 1. 2.], vel=[ 0. 1. 2.])
调用 apply_impulse 方法：
1p.apply_impulse(np.arange(3., dtype='float32'), 1.0)
2
3p
particle.Particle(mass=1.0, charge=2.0, pos=[ 0. 1.5 3. ], vel=[ 0. 2. 4.])
查看质量：
1p.mass
1.0
修改质量：
1p.mass = 3.0
查看 charge：
1p.charge
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。
1import zipfile
2
3f = zipfile.ZipFile('07-05-particle.zip','w',zipfile.ZIP_DEFLATED)
4
5names = ['particle.pyx',
6 'particle_extern.cpp',
7 'particle_extern.h',
8 'setup.py']
9for name in names:
10 f.write(name)
11
12f.close()
13
14!rm -f setup*.*
15!rm -f particle*.*
16!rm -rf build