Cython和numpy

Question

尝试运行高性能Python的示例7-11

cython_np.pyx

#cython_np.pyx
import numpy as np
cimport numpy as np
def calculate_z(int maxiter, double complex[:] zs, double complex[:] cs):
    cdef unsigned int i, n
    cdef double complex z, c
    cdef int[:] output = np.empty(len(zs), dtype = np.int32)
    for i in range(len(zs)):
        n = 0
        z = zs[i]
        c = cs[i]
        while n < maxiter and (z.real * z.real + z.imag * z.imag) < 4:
            z = z * z + c
            n  += 1
        output[i] = n
    return output

setup.py

from distutils.core import setup
from distutils.extension import Extension
from Cython.Distutils import build_ext

setup(
        cmdclass = {'build_ext':build_ext},
        ext_modules = [Extension("calculate", ["cythonfn.pyx"])]
)

在终点站，ubuntu 16.04

python3 setup.py build_ext --inplace

得到一些警告

running build_ext
cythoning cythonfn.pyx to cythonfn.c
building 'calculate' extension
x86_64-linux-gnu-gcc -pthread -DNDEBUG -g -fwrapv -O2 -Wall -Wstrict-prototypes -g -fstack-protector-strong -Wformat -Werror=format-security -Wdate-time -D_FORTIFY_SOURCE=2 -fPIC -I/usr/include/python3.5m -c cythonfn.c -o build/temp.linux-x86_64-3.5/cythonfn.o
In file included from /usr/include/python3.5m/numpy/ndarraytypes.h:1777:0,
                 from /usr/include/python3.5m/numpy/ndarrayobject.h:18,
                 from /usr/include/python3.5m/numpy/arrayobject.h:4,
                 from cythonfn.c:274:
/usr/include/python3.5m/numpy/npy_1_7_deprecated_api.h:15:2: warning:          #warning "Using deprecated NumPy API, disable it by " "#defining   NPY_NO_DEPRECATED_API NPY_1_7_API_VERSION" [-Wcpp]
 #warning "Using deprecated NumPy API, disable it by " \
  ^
In file included from /usr/include/python3.5m/numpy/ndarrayobject.h:27:0,
                 from /usr/include/python3.5m/numpy/arrayobject.h:4,
                 from cythonfn.c:274:
/usr/include/python3.5m/numpy/__multiarray_api.h:1448:1: warning: ‘_import_array’ defined but not used [-Wunused-function]
 _import_array(void)
 ^
x86_64-linux-gnu-gcc -pthread -shared -Wl,-O1 -Wl,-Bsymbolic-functions -Wl,-Bsymbolic-functions -Wl,-z,relro -Wl,-Bsymbolic-functions -Wl,-z,relro -g -fstack-protector-strong -Wformat -Werror=format-security -Wdate-time -D_FORTIFY_SOURCE=2 build/temp.linux-x86_64-3.5/cythonfn.o -o MY_DIR/calculate.cpython-35m-x86_64-linux-gnu.so

当我试图在Ipython中运行使用函数calculate.calculate.z时，它说

TypeError: a bytes-like object is required, not 'list'

使用Compuate.z的细节

对警告有什么想法吗？

Answer 1

我认为，基于http://docs.cython.org/en/latest/src/userguide/memoryviews.html中的例子

double complex[:] zs

使用double complex dtype定义一个一维内存视图。这类似于带有该dtype的numpy数组。

您的代码将列表传递给此函数。列表是Python对象，不能作为C或Cython原生数组访问。

您的源提供了如何调用此函数的任何信息吗？我拿不到那本书。

Answer 2

同样的问题发生在第二版。虽然np.asarray()可以解决这个问题，但它可能(根据我自己的实验)会在一定程度上损害代码性能。原因可能是我们需要为新创建的数组分配新的空间)。