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

[Brett Cannon]

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

> 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.

-Brett