[PyQt] Access to QSharedMemory with buffer protocol

[Giovanni Bajo]

On mar, 2010-11-02 at 13:57 +0200, Hans-Peter Jansen wrote:
> On Tuesday 02 November 2010, 11:26:46 Giovanni Bajo wrote:
> > On mar, 2010-11-02 at 10:16 +0000, Phil Thompson wrote:
> > > On Tue, 2 Nov 2010 00:00:06 +0200, "Hans-Peter Jansen"
> > > <hpj at urpla.net>
> > >
> > > wrote:
> > > > Hi Phil,
> > > >
> > > > end of July last year, Alexandre Raczynski asked about accessing
> > > > QSharedMemory, and you replied, that:
> > > >
> > > > mutable_data = buffer(sharedMemory.data())
> > > >
> > > > ...should give _write_ access to the memory.
> > >
> > > ...bad advice. I didn't realise that you can't create mutable
> > > buffers from Python. (Although there is no reason why you shouldn't
> > > be able to.)
> >
> > Actually, Python 2.7 has memoryview(); if
> > memoryview(sharedMemory.data()) worked, it would be possible to use
> > memoryview's method to mutate the buffer, without having to come up
> > with a different API for sip.voidptr.
> 
> Giovanni, isn't memoryview just a different _interface_ to the buffer 
> protocol? 

To the best of my understanding, it is a more complete interface that
also allows writable buffers. I think it is the best match to allow
access to the "contents" of a sip.voidptr and its const version.

> Anyway, being able to use QSharedMemory with 2.7 and higher 
> only looks like an arbitrary restriction to me. At least many of my 
> production systems would be locked out, then. For proper support, Phil 
> might have to do both variants of the buffer protocol anyway..

I understand your concerns. Support for memoryview (as a silent
conversion to/from void* at SIP level) would still be required for
interoperability with libraries which don't know sip.voidptr but can
use/produce a memoryview.

I was just wondering if there was a better solution than coming up with
a custom API for sip.voidptr for pre-2.7, but I can't see it.
-- 
Giovanni Bajo      ::  Develer S.r.l.
rasky at develer.com  ::  http://www.develer.com

Blog: http://giovanni.bajo.it
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