[Python-Dev] What to do for bytes in 2.6? (original) (raw)

Guido van Rossum guido at python.org
Fri Jan 18 16:00:57 CET 2008

On Jan 18, 2008 12:27 AM, Christian Heimes <lists at cheimes.de> wrote:

Guido van Rossum wrote: > Oh, you won't. Just don't use the -3 command-line flag and don't put > "from future import " at the top of your modules, and > you won't have to change your ways at all. You can continue to > distribute your packages in 2.5 syntax that will also work with 2.6, > and your users will be happy (as long as they don't want to use your > code on 3.0 -- but if you want to give them that, that is when you > will finally be forced to face the issue. :-)

from future import bytes ? What should the future statement change? * "" returns unicode instead of str * b"" is allowed and returns bytes (a new subclass of str) * u"" is still allowed and returns unicode, too. * The str built-in is not available.

I don't think any of that is necessary. I would rather have the following two in the language by default (see my response to Terry and Raymond):

bytes is an alias for str (not even a subclass) b"" is an alias for ""

> Note that I believe that the -3 flag should not change semantics -- it > should only add warnings. Semantic changes must either be backwards > compatible or be requested explicitly with a forward import (which > 2to3 can remove).

Agreed! Should the -3 flag also warn about deprecated features which can easily migrated with 2to3? In the past a warning for `` (back ticks) were added. The feature is deprecated but the migration is very simple.

Personally, I think such warnings are misguided. -3 should augment 2to3, not duplicate its work.

A 2to26 fixer may be worth implementing, too. It could migrate minor changes like `` -> repr and "except egg, spam" -> "except egg as spam".

2to3 with selected options can do that already. But again, I don't see the point -- 2.6 code can just use 2.5 syntax and 2to3 will take care of the migration.

There is only one thing I'd like -3 to warn about regarding except clauses: if the 'err' variable is used past the end of the except clause. That is a true semantic change that 2to3 cannot easily fix or flag. Consider this an example of how 2to3 and -3 should augment each other.

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

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