python与cython对应(变量、函数等)

参考：http://docs.cython.org/en/latest/

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变量

python	C/C++	cython
a=True	bool a=1/True	cdef/cpdef bint a=1
a=”2”	char* a=’2’	cdef/cpdef char* a=’2’
a=”2123bc”	char* a=”2123bc”	cdef/cpdef char* a=”2123bc”
a=2	int a=2	cdef/cpdef int a=2
a=2	short int a=2	cdef/cpdef short int a=2
a=2.0	double a=2.0	cdef/cpdef double a=2.0
a=2.0	float a=2.0	cdef/cpdef float a=2.0
a=np.zeros(10)	double[] a=np.zeros(10)	cdef/cpdef double[:] a=np.zeros(10)
a=np.zeros(10,10)	double[,] a=np.zeros(10,10)	cdef/cpdef double[:,:] a=np.zeros(10,10)

cdef int x,y,z # 政型变量
cdef char *s # 字符串/字符
cdef float x = 5.2 (single precision) 
cdef double x = 40.5 (double precision)
cdef list languages # list 列表
cdef dict abc_dict # dict 字典
cdef tuple lan # 元组
cdef object thing # 任意对象

模块导入

python	C/C++	cython
import	_	cimport
from math/cmath import exp	include math	from libc.math cimport exp

类/函数

python	C/C++	cython
class	class	cdef/cpdef cppclass
def rbf_network(X, beta, theta)	double[:] rbf_network(double[:, :] X, double[:] beta, double theta)	cdef/cpdef/def double[:] rbf_network(double[:, :] X, double[:] beta, double theta)

def, cdef, and cpdef

• def - 常规的python函数，仅来自Python的调用。
• cdef - cython只有函数，不能从python-only代码访问这些函数，必须在Cython中进行访问，因为对于这些函数将不会有C语言转换。
• cpdef - C和Python。 将为Python创建一个C函数和一个包装器。 为什么不总是使用cpdef？ 在某些情况下，你可能只有C指针，就像C数组一样。 但是，我们将主要使用cpdef。

调用C函数

参考：http://cython.readthedocs.io/en/latest/src/tutorial/external.html

In [23]: %%cython
    ...: from libc.stdlib cimport atoi
    ...: from libc.string cimport strlen
    ...: cdef char* s="1234567"
    ...: print(strlen(s))
    ...: print(atoi(s))
    ...: 
7
1234567

In [24]: %%cython
    ...: from cpython.set cimport PyAnySet_Check
    ...: a={1,2,3,4}
    ...: print(PyAnySet_Check(a))
    ...: 
True

In [25]: %%cython
    ...: from cpython.set cimport PySet_Add
    ...: a={1,2,3,4}
    ...: print(PySet_Add(a,5))
    ...: print(a)
    ...: 
0
{1, 2, 3, 4, 5}

In [28]: %%cython
    ...: from cpython.set cimport PySet_Pop
    ...: a={1,2,3,4,5}
    ...: print(PySet_Pop(a))
    ...: print(a)
    ...: 
1
{2, 3, 4, 5}

In [29]: %%cython
    ...: from numpy.math cimport PI
    ...: print(PI)
    ...: 
3.141592653589793

In [30]: %%cython
    ...: from numpy.math cimport E
    ...: print(E)
    ...: 
2.718281828459045

In [32]: %%cython
    ...: from libc.math cimport sin
    ...: cdef int a=30
    ...: print(sin(a/180))
    ...: 
0.16589613269341502

In [33]: %%cython
    ...: cdef extern from "math.h":
    ...:     double sin(double x)
    ...: print(sin(30/180))
    ...: 
0.16589613269341502

# 动态链接
from distutils.core import setup
from distutils.extension import Extension
from Cython.Build import cythonize

ext_modules=[
    Extension("demo",
              sources=["demo.pyx"],
              libraries=["m"] # Unix-like specific
    )
]

setup(
  name = "Demos",
  ext_modules = cythonize(ext_modules)
)

In [42]: %%cython
    ...: from libc.string cimport strstr
    ...: cdef char* data = "hfvcakdfagbcffvschvxcdfgccbcfhvgcsnfxjh"
    ...: pos = strstr(needle='akd', haystack=data)
    ...: print (pos)
    ...: 
b'akdfagbcffvschvxcdfgccbcfhvgcsnfxjh'


In [3]: %%cython
   ...: cdef extern from "string.h":
   ...:     char* strstr(const char *haystack, const char *needle)
   ...: cdef char* data = "hfvcakdfagbcffvschvxcdfgccbcfhvgcsnfxjh"
   ...: 
   ...: pos = strstr(needle='akd', haystack=data)
   ...: print(pos)
   ...: 
   ...: 
b'akdfagbcffvschvxcdfgccbcfhvgcsnfxjh'