[Python-3000] Implementing % formatting in terms of str.format()

[Steven Bethard]

On Sat, Apr 12, 2008 at 12:26 PM, Georg Brandl <g.brandl at gmx.net> wrote:
> Steven Bethard schrieb:
>
> > On Sat, Apr 12, 2008 at 8:26 AM,  <skip at pobox.com> wrote:
>  >>
>  >>     Nick> That's exactly the problem though - while a 2to3 fixer can be
>  >>     Nick> written for a tiny subset of formatting calls (those that meet the
>  >>     Nick> constraints you gave)...
>  >>
>  >>  In my personal experience, either the LHS will be a string literal or the
>  >>  RHS will be locals(), globals() or a tuple.  Yes, you will have a hard, if
>  >>  not impossible, time with the general x % y.  Still, I think a fixer that
>  >>  only addresses the "tiny subset" would go a long ways to converting existing
>  >>  code.  For the rest it could insert special comments so the programmer can
>  >>  grep for the problematic cases.
>  >
>  > Rather than inserting special comments, why don't we just introduce a
>  > -3 warning for using % string formatting? Then, you can use 2to3 to
>  > convert as much as it can, and you can use the -3 warning to identify
>  > any other places you're using % string formatting and fix them by
>  > hand. Adding such a -3 warning shouldn't be much more than a couple of
>  > lines at the beginning of stringobject.c:PyString_Format.
>
>  Please don't -- a Py3k warning makes no sense if the feature isn't really
>  going away in Py3k. Py3k warnings really should only warn about things
>  that are going to break in 3.0.

My understanding is that we'd break % string formatting in Py3k if we
could. The only reason we won't is that it's not generally possible to
write a 2to3 fixer. So while it won't actually break, I think
conveying our intention to break it (using a -3 warning) wouldn't be
unreasonable.

Steve
-- 
I'm not *in*-sane. Indeed, I am so far *out* of sane that you appear a
tiny blip on the distant coast of sanity.
 --- Bucky Katt, Get Fuzzy