[Python-Dev] PEP 460 reboot (original) (raw)

Donald Stufft donald at stufft.io
Mon Jan 13 23:31:33 CET 2014

On Jan 13, 2014, at 5:25 PM, Eric V. Smith <eric at trueblade.com> wrote:

On 1/13/2014 4:59 PM, Guido van Rossum wrote:

On Mon, Jan 13, 2014 at 1:29 PM, Glenn Linderman <v+python at g.nevcal.com> wrote:

If somehow (unlikely though it seems) we end up keeping %s (e.g. strictly to ease porting), we could also keep %r as an alias for %a.

%s for strictly interpolating bytes eases porting. Sad name, but good for compatibility. When the blowup happens, due to having a str type passed, the porter adds the appropriate .encode(...) to the parameter, so it doesn't blow up on Py 3, and it'll be OK for Py 2 as well, will it not? Lots of code uses %s with numbers too, and probably the occasional None or list (relying on the Python 2 near-guarantee that most objects' str() is their repr() and that repr() nearly guarantees to return only ASCII). E.g. I'm sure you can find live code doing something like headers.append('Content-Length: %s\r\n' % len(body)) That's why I think we should support %s taking bytes, int, float. And make %b mean the same thing, if you want. But I think we need to keep %s (however limited) for compatibility with Python 2. Personally, I'd be okay with %s not accepting str (by raising an exception). I think that would give us a large "compatibility surface" in common with Python 2.

%s not accepting str is the major thing I’d personally be against. %s taking numeric types and bytes would be fine. The main thing i’d be worried about is where the RHS may possibly contain something non ASCII that needs encoding (such as the str case).

Donald Stufft PGP: 0x6E3CBCE93372DCFA // 7C6B 7C5D 5E2B 6356 A926 F04F 6E3C BCE9 3372 DCFA

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