Cython MemoryViews:使用数组参数包装C函数以传递numpy数组 [英] Cython memoryviews: wrapping c function with array parameter to pass numpy array
问题描述
我正在尝试使用Cython用数组参数( quick_sort()
)包装c函数,因此可以将numpy数组传递给它。我已经在文档,SO和网络中搜索了一个可行的最小示例,但没有找到。我尝试了几种可能性,但没有任何进展,因此请帮助我解决这个问题。这是我的文件:
quicksort.c
#include< stdio.h>
void quick_sort(int * a,int n){
int i,j,p,t;
,如果(n <2)
回报;
p = a [n / 2];
for(i = 0,j = n-1 ;; i ++,j--){
而(a [i]< p)
i ++;
而(p j--;
如果(i> = j)
休息;
t = a [i];
a [i] = a [j];
a [j] = t;
}
quick_sort(a,i);
quick_sort(a + i,n-i);
}
quicksort.h
void quick_sort(int * a,int n);
quicksort.pxd
cdef extern来自 quicksort.h:
void quick_sort(int [:] a,int n)
cy_quicksort.pyx
cimport quicksort
def quicksort_c(int [:] a):
quicksort.quick_sort(a,a.size)
设置。 py
来自distutils.core导入设置,来自Cython的
。构建导入cythonize
的设置(
name ='quicksort cython',
ext_modules = cythonize( *。pyx),
)
当我运行 python setup.py build_ext --inplace
命令时,它返回以下错误:
cy_quicksort.c:1362:14:错误:将'__Pyx_memviewslice'传递给
不兼容类型'int *'
quick_sort(__ pyx_v_a,__pyx_t_3)的参数;
^ ~~~~~~~~
./quicksort.h:1:23:注意:在此处将参数传递给参数'a'
void quick_sort(int * a,int n );
我要实现的是对此进行编译并能够运行:
从cy_quicksort导入numpy作为np
导入quicksort_c
a = np.array(range(9,0,-1),dtype = np.int32)
quicksort_c(a)
谢谢您的时间!
编辑:
在DavidW建议在 quicksort.pxd , cy_quicksort.pyx 中进行更改并进行更改后 setup.py 文件转换为以下格式,即可正常工作。
setup.py
从distutils.core导入设置
从cyutil.com中的
。从distutils.extension导入import cythonize
'cy_quicksort.pyx','quicksort.c']
扩展名= [Extension( cy_quicksort,源文件)]
setup(
ext_modules = cythonize (扩展名)
)
问题主要出在 quicksort.pxd-定义需要与quicksort.h中的匹配:
cdef extern from quicksort.h:
void quick_sort(int * a,int n)
(< [:]
而是将其定义为memoryview,这是Cythony的发明,不能直接转换为指针,如您的错误所述)。 / p>
然后您需要从 cy_quicksort.pyx中的内存视图中获取一个指针
def quicksort_c(int [:: 1] a):
quicksort.quick_sort(& a [0],a.size)#获取第一个元素的地址
我将输入参数更改为 [:: 1]
来指定元素必须在内存中是连续的,我认为这是quicksort所期望的。
(注意-未经测试,但是相当简单,应该可以使用!)
I am trying to use Cython to wrap c function with an array parameter (quick_sort()
), so I can pass a numpy array to it. I've searched the documentation, SO and web for a working, minimal example but didn't find it. I've tried several possibilities but without any progress, so please help me to figure it out. Here are my files:
quicksort.c
#include <stdio.h>
void quick_sort (int* a, int n) {
int i, j, p, t;
if (n < 2)
return;
p = a[n / 2];
for (i = 0, j = n - 1;; i++, j--) {
while (a[i] < p)
i++;
while (p < a[j])
j--;
if (i >= j)
break;
t = a[i];
a[i] = a[j];
a[j] = t;
}
quick_sort(a, i);
quick_sort(a + i, n - i);
}
quicksort.h
void quick_sort (int* a, int n);
quicksort.pxd
cdef extern from "quicksort.h":
void quick_sort (int[:] a, int n)
cy_quicksort.pyx
cimport quicksort
def quicksort_c(int[:] a):
quicksort.quick_sort(a, a.size)
setup.py
from distutils.core import setup
from Cython.Build import cythonize
setup(
name='quicksort cython',
ext_modules=cythonize("*.pyx"),
)
When I'm running python setup.py build_ext --inplace
command, it returns the following error:
cy_quicksort.c:1362:14: error: passing '__Pyx_memviewslice' to parameter of
incompatible type 'int *'
quick_sort(__pyx_v_a, __pyx_t_3);
^~~~~~~~~
./quicksort.h:1:23: note: passing argument to parameter 'a' here
void quick_sort (int* a, int n);
What I want to achieve is to compile this and be able to run for example:
import numpy as np
from cy_quicksort import quicksort_c
a = np.array(range(9, 0, -1), dtype=np.int32)
quicksort_c(a)
Thanks in advance for Your time!
Edit:
After changes suggested by DavidW in quicksort.pxd, cy_quicksort.pyx and changing the setup.py file into the following form, it's working as intended.
setup.py
from distutils.core import setup
from Cython.Build import cythonize
from distutils.extension import Extension
sourcefiles = ['cy_quicksort.pyx', 'quicksort.c']
extensions = [Extension("cy_quicksort", sourcefiles)]
setup(
ext_modules = cythonize(extensions)
)
The problem is mainly in "quicksort.pxd" - the definition needs to match that in quicksort.h:
cdef extern from "quicksort.h":
void quick_sort (int* a, int n)
([:]
defines it as a memoryview instead, which is a Cythony invention and can't be cast directly to a pointer, as your error says).
You then need to get a pointer from the memoryview in "cy_quicksort.pyx"
def quicksort_c(int[::1] a):
quicksort.quick_sort(&a[0], a.size) # get address of first element
I've changed the input parameter to [::1]
to specify that the elements must be continuous in memory, which I think is what quicksort expects.
(Note - untested, but reasonably simple so should work!)
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