[Cython] Can't assign numpy array to memoryview

[Dave Hirschfeld]

Dave Hirschfeld <dave.hirschfeld at ...> writes:

> 
> It appears that you can't assign an ndarray to a memoryview slice? Is 
> this correct/expected behaviour?
> 
> Whilst there are a couple of possible workarounds it would be nice if 
> this just worked as it's a slightly surprising deviation from the 
> ndarray behaviour.
> 
> Broken example:
> ```
> In [3]: %%cython
>    ...: cimport cython
>    ...: import numpy as np
>    ...: cimport numpy as np
>    ...: 
>    ...: cpdef np.ndarray[np.float64_t, ndim=2] f():
>    ...:     cdef np.ndarray[np.float64_t, ndim=2] x = np.ones([3, 4], 
> dtype=np.float64)
>    ...:     cdef double[:,:] y = np.zeros([3, 4], dtype=np.float64)
>    ...:     cdef np.ndarray[np.float64_t, ndim=1] row
>    ...:     cdef int idx
>    ...:     for idx, row in enumerate(x):
>    ...:         y[idx] = row
>    ...:     return np.asarray(y)
> 
> In [4]: f()
> Traceback (most recent call last):
> 
>   File "<ipython-input-4-0ec059b9bfe1>", line 1, in <module>
>     f()
> 
>   File "_cython_magic_5f2586693ddbf044815dae01d800bc0c.pyx", line 5, 
in 
> _cython_magic_5f2586693ddbf044815dae01d800bc0c.f 
> 
(C:\Users\dhirschfeld\.ipython\cython\_cython_magic_5f2586693ddbf044815d
> ae01d800bc0c.c:2086)
> 
>   File "_cython_magic_5f2586693ddbf044815dae01d800bc0c.pyx", line 11, 
in 
> _cython_magic_5f2586693ddbf044815dae01d800bc0c.f 
> 
(C:\Users\dhirschfeld\.ipython\cython\_cython_magic_5f2586693ddbf044815d
> ae01d800bc0c.c:1935)
> ```

The error which I cutoff above is:

Traceback (most recent call last):

  File "<ipython-input-4-0ec059b9bfe1>", line 1, in <module>
    f()

  File "_cython_magic_5f2586693ddbf044815dae01d800bc0c.pyx", line 5, in 
_cython_magic_5f2586693ddbf044815dae01d800bc0c.f 
(C:\Users\dhirschfeld\.ipython\cython\_cython_magic_5f2586693ddbf044815d
ae01d800bc0c.c:2086)

  File "_cython_magic_5f2586693ddbf044815dae01d800bc0c.pyx", line 11, in 
_cython_magic_5f2586693ddbf044815dae01d800bc0c.f 
(C:\Users\dhirschfeld\.ipython\cython\_cython_magic_5f2586693ddbf044815d
ae01d800bc0c.c:1935)

TypeError: only length-1 arrays can be converted to Python scalars