如何在 cython 中从 c 数组公开一个 numpy 数组？

Question

cpdef myf():
    # pd has to be a c array.
    # Because it will then be consumed by some c function.
    cdef double pd[8000]
    # Do something with pd
    ...
    # Get a memoryview.
    cdef double[:] pd_view = pd 
    # Coercion the memoryview to numpy array. Not working.
    ret = np.asarray(pd)
    return ret

我想 return 一个 numpy 数组。我该怎么做？

目前我要做的

pd_np = np.zeros(8000, dtype=np.double)
cdef int i
for i in range(8000):
    pd_np[i] = pd[i]

Answer 1

在此处的 memview 示例中 http://docs.cython.org/src/userguide/memoryviews.html

# Memoryview on a C array
cdef int carr[3][3][3]
cdef int [:, :, :] carr_view = carr
carr_view[...] = narr_view  # np.arange(27, dtype=np.dtype("i")).reshape((3, 3, 3))
carr_view[0, 0, 0] = 100

我可以从 carr_view、carr 上的内存视图、C 数组创建一个 numpy 数组。

# print np.array(carr)    # cython error
print 'numpy array on carr_view'
print np.array(carr_view)
print np.array(carr_view).sum()   # match sum3d(carr)
# or np.asarray(carr_view)


print 'numpy copy from carr_view'
carr_copy = np.empty((3,3,3))
carr_copy[...] = carr_view[...]  # don't need indexed copy
print carr_copy
print carr_copy.sum()   # match sum3d(carr)

Answer 2

如果你只是在你的函数中声明你的数组为什么不让它成为一个 numpy 数组开始，那么当你需要 c 数组时你可以只获取数据指针。

cimport numpy as np
import numpy as np

def myf():
    cdef np.ndarray[double, ndim=1, mode="c"] pd_numpy = np.empty(8000)
    cdef double *pd = &pd_numpy[0]

    # Do something to fill pd with values
    for i in range(8000):
        pd[i] = i

    return pd_numpy

Answer 3

我打错了， ret = np.asarray(pd_view) 有效

如何在 cython 中从 c 数组公开一个 numpy 数组？

How to expose a numpy array from c array in cython?

python

numpy

cython