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394 lines
10 KiB
Markdown
394 lines
10 KiB
Markdown
# Cython：class 和 cdef class，使用 C++
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## class 和 cdef class
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`class` 定义属性变量比较自由，`cdef class` 可以定义 `cdef`
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`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。
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`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。
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`__dealloc__` 函数类似析构函数，负责释放申请的内存。
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`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：
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```py
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property name:
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def __get__(self):
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return something
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def __set__(self):
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set_something
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```
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## 使用 C++ 类
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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。
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假设我们有这样一个 `C++` 类：
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In [1]:
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```py
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%%file particle_extern.h
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#ifndef _PARTICLE_EXTERN_H_
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#define _PARTICLE_EXTERN_H_
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class Particle {
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public:
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Particle() :
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mass(0), charge(0) {}
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Particle(float m, float c, float *p, float *v);
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~Particle() {}
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float getMass() {return mass; }
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void setMass(float m) { mass = m; }
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float getCharge() { return charge; }
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const float *getVel() { return vel; }
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const float *getPos() { return pos; }
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void applyImpulse(float *f, float t);
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private:
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float mass, charge;
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float pos[3], vel[3];
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};
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#endif
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```
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```py
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Overwriting particle_extern.h
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```
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In [2]:
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```py
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%%file particle_extern.cpp
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#include "particle_extern.h"
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Particle::Particle(float m, float c, float *p, float *v) :
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mass(m), charge(c)
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{
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for (int i=0; i<3; ++i) {
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pos[i] = p[i]; vel[i] = v[i];
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}
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}
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void Particle::applyImpulse(float *f, float t)
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{
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float newvi;
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for(int i=0; i<3; ++i) {
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newvi = vel[i] + t / mass * f[i];
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pos[i] = (newvi + vel[i]) * t / 2.;
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vel[i] = newvi;
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}
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}
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```
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```py
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Overwriting particle_extern.cpp
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```
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在 `Cython` 中调用这个类：
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In [3]:
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```py
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%%file particle.pyx
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import numpy as np
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cdef extern from "particle_extern.h":
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cppclass _Particle "Particle":
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_Particle(float m, float c, float *p, float *v)
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float getMass()
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void setMass(float m)
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float getCharge()
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const float *getVel()
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const float *getPos()
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void applyImpulse(float *f, float t)
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cdef class Particle:
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cdef _Particle *thisptr # ptr to C++ instance
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def __cinit__(self, m, c, float[::1] p, float[::1] v):
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if p.shape[0] != 3 or v.shape[0] != 3:
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raise ValueError("...")
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self.thisptr = new _Particle(m, c, &p[0], &v[0])
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def __dealloc__(self):
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del self.thisptr
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def apply_impulse(self, float[::1] v, float t):
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self.thisptr.applyImpulse(&v[0], t)
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def __repr__(self):
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args = ', '.join('%s=%s' % (n, getattr(self, n)) for n in ('mass', 'charge', 'pos', 'vel'))
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return 'particle.Particle(%s)' % args
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property charge:
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def __get__(self):
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return self.thisptr.getCharge()
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property mass: # Cython-style properties.
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def __get__(self):
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return self.thisptr.getMass()
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def __set__(self, m):
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self.thisptr.setMass(m)
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property vel:
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def __get__(self):
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cdef const float *_vel = self.thisptr.getVel()
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cdef float[::1] arr = np.empty((3,), dtype=np.float32)
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for i in range(3):
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arr[i] = _vel[i]
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return np.asarray(arr)
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property pos:
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def __get__(self):
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cdef const float *_pos = self.thisptr.getPos()
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cdef float[::1] arr = np.empty((3,), dtype=np.float32)
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for i in range(3):
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arr[i] = _pos[i]
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return np.asarray(arr)
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```
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```py
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Overwriting particle.pyx
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```
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首先从头文件声明这个类：
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```py
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cdef extern from "particle_extern.h":
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cppclass _Particle "Particle":
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_Particle(float m, float c, float *p, float *v)
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float getMass()
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void setMass(float m)
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float getCharge()
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const float *getVel()
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const float *getPos()
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void applyImpulse(float *f, float t)
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```
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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`。
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```py
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cdef class Particle:
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cdef _Particle *thisptr
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def __cinit__(self, m, c, float[::1] p, float[::1] v):
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if p.shape[0] != 3 or v.shape[0] != 3:
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raise ValueError("...")
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self.thisptr = new _Particle(m, c, &p[0], &v[0])
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```
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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。
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In [4]:
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```py
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%%file setup.py
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from distutils.core import setup
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from distutils.extension import Extension
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from Cython.Distutils import build_ext
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ext = Extension("particle", ["particle.pyx", "particle_extern.cpp"], language="c++")
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setup(
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cmdclass = {'build_ext': build_ext},
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ext_modules = [ext],
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)
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```
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```py
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Overwriting setup.py
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```
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要加上 `language="c++"` 的选项，然后编译：
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In [5]:
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```py
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!python setup.py build_ext -i
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```
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```py
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running build_ext
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cythoning particle.pyx to particle.cpp
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building 'particle' extension
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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
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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
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writing build\temp.win-amd64-2.7\Release\particle.def
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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"
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```
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```py
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particle.cpp: In function 'void __Pyx_RaiseArgtupleInvalid(const char*, int, Py_ssize_t, Py_ssize_t, Py_ssize_t)':
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particle.cpp:14931:59: warning: unknown conversion type character 'z' in format [-Wformat]
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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]
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particle.cpp:14931:59: warning: unknown conversion type character 'z' in format [-Wformat]
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particle.cpp:14931:59: warning: too many arguments for format [-Wformat-extra-args]
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particle.cpp: In function 'int __Pyx_BufFmt_ProcessTypeChunk(__Pyx_BufFmt_Context*)':
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particle.cpp:15498:78: warning: unknown conversion type character 'z' in format [-Wformat]
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particle.cpp:15498:78: warning: unknown conversion type character 'z' in format [-Wformat]
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particle.cpp:15498:78: warning: too many arguments for format [-Wformat-extra-args]
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particle.cpp:15550:67: warning: unknown conversion type character 'z' in format [-Wformat]
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particle.cpp:15550:67: warning: unknown conversion type character 'z' in format [-Wformat]
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particle.cpp:15550:67: warning: too many arguments for format [-Wformat-extra-args]
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particle.cpp: In function 'PyObject* __pyx_buffmt_parse_array(__Pyx_BufFmt_Context*, const char**)':
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particle.cpp:15612:69: warning: unknown conversion type character 'z' in format [-Wformat]
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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]
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particle.cpp:15612:69: warning: too many arguments for format [-Wformat-extra-args]
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particle.cpp: In function 'int __Pyx_GetBufferAndValidate(Py_buffer*, PyObject*, __Pyx_TypeInfo*, int, int, int, __Pyx_BufFmt_StackElem*)':
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particle.cpp:15797:73: warning: unknown conversion type character 'z' in format [-Wformat]
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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]
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particle.cpp:15797:73: warning: unknown conversion type character 'z' in format [-Wformat]
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particle.cpp:15797:73: warning: too many arguments for format [-Wformat-extra-args]
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particle.cpp: In function 'void __Pyx_RaiseTooManyValuesError(Py_ssize_t)':
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particle.cpp:16216:94: warning: unknown conversion type character 'z' in format [-Wformat]
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particle.cpp:16216:94: warning: too many arguments for format [-Wformat-extra-args]
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particle.cpp: In function 'void __Pyx_RaiseNeedMoreValuesError(Py_ssize_t)':
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particle.cpp:16222:48: warning: unknown conversion type character 'z' in format [-Wformat]
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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]
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particle.cpp:16222:48: warning: too many arguments for format [-Wformat-extra-args]
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particle.cpp: In function 'int __Pyx_ValidateAndInit_memviewslice(int*, int, int, int, __Pyx_TypeInfo*, __Pyx_BufFmt_StackElem*, __Pyx_memviewslice*, PyObject*)':
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particle.cpp:16941:50: warning: unknown conversion type character 'z' in format [-Wformat]
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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]
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particle.cpp:16941:50: warning: unknown conversion type character 'z' in format [-Wformat]
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particle.cpp:16941:50: warning: too many arguments for format [-Wformat-extra-args]
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```
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In [6]:
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```py
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import particle
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```
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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：
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In [7]:
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```py
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import numpy as np
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pos = vel = np.arange(3., dtype='float32')
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mass = 1.0
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charge = 2.0
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p = particle.Particle(mass, charge, pos, vel)
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p
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```
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Out[7]:
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```py
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particle.Particle(mass=1.0, charge=2.0, pos=[ 0\. 1\. 2.], vel=[ 0\. 1\. 2.])
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```
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调用 `apply_impulse` 方法：
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In [8]:
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```py
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p.apply_impulse(np.arange(3., dtype='float32'), 1.0)
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p
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```
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Out[8]:
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```py
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particle.Particle(mass=1.0, charge=2.0, pos=[ 0\. 1.5 3\. ], vel=[ 0\. 2\. 4.])
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```
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查看质量：
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In [9]:
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```py
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p.mass
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```
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Out[9]:
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```py
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1.0
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```
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修改质量：
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In [10]:
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```py
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p.mass = 3.0
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```
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查看 `charge`：
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In [11]:
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```py
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p.charge
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```
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Out[11]:
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```py
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2.0
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```
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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。
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In [12]:
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```py
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import zipfile
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f = zipfile.ZipFile('07-05-particle.zip','w',zipfile.ZIP_DEFLATED)
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names = ['particle.pyx',
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'particle_extern.cpp',
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'particle_extern.h',
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'setup.py']
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for name in names:
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f.write(name)
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f.close()
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!rm -f setup*.*
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!rm -f particle*.*
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!rm -rf build
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``` |