[Python-Dev] RFC: PEP 460: Add bytes % args and bytes.format(args) to Python 3.5 (original) (raw)

Nick Coghlan ncoghlan at gmail.com
Mon Jan 6 15:45:58 CET 2014

On 6 Jan 2014 22:15, "Brett Cannon" <brett at python.org> wrote:

On Mon, Jan 6, 2014 at 8:59 AM, Antoine Pitrou <solipsis at pitrou.net> wrote: On Tue, 7 Jan 2014 00:54:17 +1100 Chris Angelico <rosuav at gmail.com> wrote: > On Tue, Jan 7, 2014 at 12:44 AM, Antoine Pitrou <solipsis at pitrou.net> wrote: > > BTW, there's a subtlety here: %s currently means "insert the result > > of calling str", but bytes formatting should not call str. > > Since it derives from the C printf notation, it means "insert string > here". The fact that str will be called is secondary to that. I > would say it's not a problem for bytes formatting to call bytes, > or in some other way convert to bytes without calling str. > > Will it be confusing to have bytes and str supporting distinctly > different format operations? Might it be better to instead create a > separate and very different method on a bytes, just to emphasize the > difference? The people who want bytes formatting, AFAICT, want something that is reasonably 2.x-compatible. That means using the same method / operator and calling conventions. Right, but that also doesn't mean that a library from the Cheeseshop couldn't be provided which works around any Python 2/3 differences. But my suspicion is anyone requesting this feature (e.g. Mercurial) want it implemented in C for performance and so some pure Python library to help with this won't get any traction.

Right, but it seems to me that a new helper module that could be made backwards compatible at least as far as 2.6 (if not further) would be more useful for that than a builtin change that won't be available until 2015. I think we have enough experience with Python 3 now to say yes, there are still some significant gaps in the support it offers for wire protocol development.

We have been hoping others would volunteer to fill that gap, but it's getting to the point where we need to start thinking about handling it ourselves by providing a hybrid Python/C helper module specifically for wire protocol programming.

An encodedstr type wouldn't implicitly interoperate with the builtins (until we finally fix the sequence operand coercion bug in CPython) but could at least handle formatting operations like this.

Cheers, Nick.

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