On 21/06/2010 17:46, P.J. Eby wrote:
At 10:51 PM 6/21/2010 +1000, Nick Coghlan wrote:
It may be that there are places where we need to rewrite standard
library algorithms to be bytes/str neutral (e.g. by using length one
slices instead of indexing). It may be that there are more APIs that
need to grow "encoding" keyword arguments that they then pass on to
the functions they call or use to convert str arguments to bytes (or
vice-versa). But without people trying to port affected libraries and
reporting bugs when they find issues, the situation isn't going to
improve.
Now, if these bugs are already being reported against 3.1 and just
aren't getting fixed, that's a completely different story...
The overall impression, though, is that this isn't really a step
forward. Now, bytes are the special case instead of unicode, but that
special case isn't actually handled any better by the stdlib - in
fact, it's arguably worse. And, the burden of addressing this seems to
have been shifted from the people who made the change, to the people
who are going to use it. But those people are not necessarily in a
position to tell you anything more than, "give me something that works
with bytes".
What I can tell you is that before, since string constants in the
stdlib were ascii bytes, and transparently promoted to unicode, stdlib
behavior was *predictable* in the presence of special cases: you got
back either bytes or unicode, but either way, you could idempotently
upgrade the result to unicode, or just pass it on. APIs were "str
safe, unicode aware". If you passed in bytes, you weren't going to get
unicode without a warning, and if you passed in unicode, it'd work and
you'd get unicode back.
Now, the APIs are neither safe nor aware -- if you pass bytes in, you
get unpredictable results back.
Ironically, it almost *would* have been better if bytes simply didn't
work as strings at all, *ever*, but if you could wrap them with a
bstr() to *treat* them as text. You could still have restrictions on
combining them, as long as it was a restriction on the unicode you
mixed with them. That is, if you could combine a bstr and a str if the
*str* was restricted to ASCII.
If we had the Python 3 design discussions to do over again, I think I
would now have stuck with the position of not letting bytes be
string-compatible at all, and instead proposed an explicit bstr()
wrapper/adapter to use them as strings, that would (in that case)
force coercion in the direction of bytes rather than strings. (And
bstr need not have been a builtin - it could have been something you
import, to help discourage casual usage.)
Might this approach lead to some people doing things wrong in the case
of porting? Sure. But there'd be little reason to use it in new code
that didn't have a real need for bytestring manipulation.
It might've been a better balance between practicality and purity, in
that it keeps the language pure, while offering a practical way to
deal with things in bytes if you really need to. And, bytes wouldn't
silently succeed *some* of the time, leading to a trap. An easy
inconsistency is worse than a bit of uniform chicken-waving.
Is it too late to make that tradeoff? Probably. Certainly it's not
practical to *implement* outside the language core, and removing
string methods would fux0r anybody whose currently-ported code relies
on bytes objects having string-like methods.
Why is your proposed bstr wrapper not practical to implement outside the
core and use in your own libraries and frameworks?
Michael
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