[Python-3000] patch: bytes object PyBUF_LOCKDATA read-only and immutable support

[Guido van Rossum]

That's a huge patch to land so close before a release. I'm not sure I
like the immutability API -- it won't be useful unless we add a hash
method, and then we have all sorts of difficulties again -- the
distinction between a hashable and an unhashable object should be made
by type, not by value (tuples containing unhashable values
notwithstanding).

I don't understand the comment about using PyBUF_WRITABLE in
_getbuffer() -- this is only used for data we're *reading* and I don't
think the GIL is even released while we're reading such things.

If you think it's important to get this in the 3.0a1 release, we
should pair-program on it ASAP, preferable tomorrow morning.
Otherwise, let's do a review next week.

--Guido

On 8/29/07, Gregory P. Smith <greg at krypto.org> wrote:
> Attached is what I've come up with so far.  Only a single field is
> added to the PyBytesObject struct.  This adds support to the bytes
> object for PyBUF_LOCKDATA buffer API operation.  bytes objects can be
> marked temporarily read-only for use while the buffer api has handed
> them off to something which may run without the GIL (think IO).  Any
> attempt to modify them during that time will raise an exception as I
> believe Martin suggested earlier.
>
> As an added bonus because its been discussed here, support for setting
> a bytes object immutable has been added since its pretty trivial once
> the read only export support was in place.  Thats not required but was
> trivial to include.
>
> I'd appreciate any feedback.
>
> My TODO list for this patch:
>
>  0. Get feedback and make adjustments as necessary.
>
>  1. Deciding between PyBUF_SIMPLE and PyBUF_WRITEABLE for the internal
>     uses of the _getbuffer() function.  bytesobject.c contains both readonly
>     and read-write uses of the buffers, i'll add boolean parameter for
>     that.
>
>  2. More testing: a few tests in the test suite fail after this but the
>     number was low and I haven't had time to look at why or what the
>     failures were.
>
>  3. Exporting methods suggested in the TODO at the top of the file.
>
>  4. Unit tests for all of the functionality this adds.
>
> NOTE: after these changes I had to make clean and rm -rf build before
> things would not segfault on import.  I suspect some things (modules?)
> were not properly recompiled after the bytesobject.h struct change
> otherwise.
>
> -gps
>
>
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-- 
--Guido van Rossum (home page: http://www.python.org/~guido/)