[Cython] MemoryViews require writeable arrays?

[Dave Hirschfeld]

Sturla Molden <sturla at ...> writes:

> 
> On 27.02.2013 20:05, Dave Hirschfeld wrote:
> 
> > Is this a required restriction? Is there any workaround?
> 
> http://www.python.org/dev/peps/pep-3118/
> 
> What you should consider is the "readonly" field in "struct bufferinfo" 
> or the access flag "PyBUF_WRITEABLE".
> 
> In short:
> 
> A PEP3118 buffer can be readonly, and then you shouldn't write to it! 
> When you set the readonly flag, Cython cannot retrieve the buffer with 
> PyBUF_WRITEABLE. Thus, Cython helps you not to shoot yourself in the 
> foot. I don't think you can declare a read-only memoryview in Cython. 
> (Well, not by any means I know of.)
> 
> Sturla
> 
> 

So the issue is that at present memoryviews can't be readonly? Presumably 
because this works for numpy arrays it would be possible to also make readonly 
memoryviews? I think that would certainly be nice to have, but maybe it's a
niche use case. 

Certainly, for IPython.parallel use it's easy enough to write a shim which sets 
the array to writeable with the understanding that changes don't get propagated 
back.

Thanks,
Dave