[Python-3000] Immutable bytes -- looking for volunteer (original) (raw)

Guido van Rossum guido at python.org
Wed Sep 26 02:22:39 CEST 2007

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/)

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