Acessing data buffer of typed memoryview in Cython

Question

I have a function expecting array pointers in Cython, e.g. with the signature

cdef void foo(DTYPE_t* x)

and a function which receives a typed memoryview from which I would like to call the first function, e.g.:

def bar(DTYPE_t[:,::1] X not None):
    foo(X[0])

Which naturally does not even compile. I've been trying for some hours now to figure out a way to access the data pointer underlying the memory view i.e. something like X.data.

Is there a way to achieve this? I sadly can not adept foo to accept memoryviews.

score 4 · Accepted Answer · answered Feb 20 '15 at 19:49

4

You want this:

foo(&X[0,0])

answered Feb 20 '15 at 19:49

Sturla Molden

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loli · Answer 2 · 2015-02-20T20:11:04.393

2

The solution is that simple, it's quite embarrassing

&X[i,j]

i.e. the call will become

foo(&X[i,0])

Which, by the way, also works with the old style numpy arrays, which are initialized like

object[int, ndim=2, mode='strided'] X

PS: If you would like to pass C-array, X[i][j] would be required, which equally works for typed memoryviews.

edited Feb 20 '15 at 20:11

answered Feb 19 '15 at 16:23

loli

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Use ```X[i,j]``` not ```X[i][j]``` – Sturla Molden Feb 20 '15 at 19:50
You are of course right. I've opted for `X[i][j]` because this syntax would work equally for C arrays. I am going to edit my answer. – loli Feb 20 '15 at 20:09

Acessing data buffer of typed memoryview in Cython

2 Answers2