On Tue, 7 Jan 2014 00:54:17 +1100
Chris Angelico <rosuav@gmail.com> wrote:
> On Tue, Jan 7, 2014 at 12:44 AM, Antoine Pitrou <solipsis@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. 
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On Mon, Jan 6, 2014 at 8:59 AM, Antoine Pitrou <solipsis@pitrou.net> wrote:
On Tue, 7 Jan 2014 00:54:17 +1100
Chris Angelico <rosuav@gmail.com> wrote:
\> On Tue, Jan 7, 2014 at 12:44 AM, Antoine Pitrou <solipsis@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.