[Python-Dev] PEP 332 revival in coordination with pep 349? [ Was:Re: release plan for 2.5 ?]

[Guido van Rossum]

On 2/14/06, Neil Schemenauer <nas at arctrix.com> wrote:
> People could spell it bytes(s.encode('latin-1')) in order to make it
> work in 2.X.  That spelling would provide a way of ensuring the type
> of the return value.

At the cost of an extra copying step.

[Guido]
> > You missed the part where I said that introducing the bytes type
> > *without* a literal seems to be a good first step. A new type, even
> > built-in, is much less drastic than a new literal (which requires
> > lexer and parser support in addition to everything else).
>
> Are you concerned about the implementation effort?  If so, I don't
> think that's justified since adding a new string prefix should be
> pretty straightforward (relative to rest of the effort involved).

Not so much the implementation but also the documentation, updating
3rd party Python preprocessors, etc.

> Are you comfortable with the proposed syntax?

Not entirely, since I don't know what b"abc<euro>def" would mean
(where <euro> is a Unicode Euro character typed in whatever source
encoding was used).

Instead of b"abc" (only ASCII) you could write bytes("abc"). Instead
of b"\xf0\xff\xee" you could write bytes([0xf0, 0xff, 0xee]).

The key disconnect for me is that if bytes are not characters, we
shouldn't use a literal notation that resembles the literal notation
for characters. And there's growing consensus that a bytes type should
be considered as an array of (8-bit unsigned) ints.

Also, bytes objects are (in my mind anyway) mutable. We have no other
literal notation for mutable objects. What would the following code
print?

  for i in range(2):
    b = b"abc"
    print b
    b[0] = ord("A")

Would the second output line print abc or Abc?

I guess the only answer that makes sense is that it should print abc
both times; but that means that b"abc" must be internally implemented
by creating a new bytes object each time. Perhaps the implementation
effort isn't so minimal after all...

(PS why is there a reply-to in your email the excludes you from the
list of recipients but includes me?)

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