[Python-3000] Immutable bytes -- looking for volunteer

[Guido van Rossum]

On 9/25/07, Brett Cannon <brett at python.org> wrote:
> On 9/25/07, Guido van Rossum <guido at python.org> wrote:
> > OK, Jeffrey's and Adam's patches were helpful; it looks like the
> > damage done by making bytes immutable is pretty limited: plenty of
> > modules are affected, but the changes are straightforward and
> > localized.
> >
> > So now I have an idea that goes a little farther. It relates to
> > Talin's response (second message in this thread if you're using gmail)
> > and acknowledges that there are some good use cases for mutable bytes
> > as well (as I've always maintained).
> >
> > How about we take the existing PyString implementation (Python 2's
> > str, currently still present as str8 in py3k), remove the locale and
> > unicode mixing support, and call it bytes. Then the PyBytes type can
> > be renamed to buffer. It is well-documented that I don't care much
> > about the existing buffer() builtin; it can be renamed to memview for
> > all I care (that would be a more descriptive name anyway).
> >
> > This would provide a much better transitional path for 2.x code
> > manipulating raw bytes using str instances: just change "..." into
> > b"..." and str into bytes. (Of course, 2.x code that is confused about
> > bytes vs. characters will fail hard in 3.0 as soon as a bytes and a
> > str instance meet -- this is already the case in the current 3.0 code
> > base and will remain unchanged.)
> >
> > It would mean more fixes beyond what Jeffrey and Adam did, since
> > iterating over a bytes instance would return a bytes instance of
> > length 1 instead of a small int, and the bytes constructor would
> > change accordingly (no more initializing a bytes object from a list of
> > ints).
> >
>
> +0.  While 2to3 would be able to help more, the methods that will be
> ripped out will make the ease in transition from this a lot less.

Compared to what? The methods to be ripped out are already not
available on bytes objects.

> Plus you can have immutable bytes in a way by passing the current
> bytes to tuple.

At what cost? tuple(b"x"*100) is a tuple of length 100.

> > The (new) buffer object would also have to change to be more
> > compatible with the (new) bytes object -- bytes<-->buffer conversions
> > should be 1-1, and iterating over a buffer instance would also have to
> > return a length-1 buffer (or bytes???) instance.
>
> Return a byte.  If you want a mutable length-1 thing you should have
> to do a length 1 slice.  Otherwise its an index operation and you want
> what is stored at the index, which is an immutable byte.

OK. Though it's questionable even whether a slice of a mutable bytes
object should return a mutable bytes object (as it is not a shared
view). But as that is what PyBytes currently do it is certainly the
easiest...

-- 
--Guido van Rossum (home page: http://www.python.org/~guido/)