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[Python-Dev] PEP 461 - Adding % and {} formatting to bytes

Nick Coghlan ncoghlan at gmail.com
Tue Jan 14 23:17:31 CET 2014 
On 15 Jan 2014 07:36, "Ethan Furman" <ethan at stoneleaf.us> wrote:
>
> On 01/14/2014 12:57 PM, Antoine Pitrou wrote:
>>
>> On Tue, 14 Jan 2014 11:56:25 -0800
>> Ethan Furman <ethan at stoneleaf.us> wrote:
>>>
>>>
>>> %s, because it is the most general, has the most convoluted resolution:
>>>
>>>     - input type is bytes?
>>>       pass it straight through
>>
>>
>> It should try to get a Py_buffer instead.
>
>
> Meaning any bytes or bytes-subtype will support the Py_buffer protocol,
and this should be the first thing we try?
>
> Sounds good.
>
> For that matter, should the first test be "does this object support
Py_buffer" and not worry about it being isinstance(obj, bytes)?

Yep. I actually suggest adjusting the %s handling to:

- interpolate Py_buffer exporters directly
- interpolate __bytes__ if defined
- reject anything with an "encode" method
- otherwise interpolate str(obj).encode("ascii")

>>>     - input type is numeric?
>>>       use its __xxx__ [1] [2] method and ascii-encode it (strictly)
>>
>>
>> What is the definition of "numeric"?
>
>
> That is a key question.

As suggested above, I would flip the question and explicitly *disallow*
implicit encoding of any object with its own "encode" method, while
allowing everything else.

Cheers,
Nick.

>
> Obviously we have int, float, and complex.  We also have Decimal.
>
> But what about Fraction?  Or some users numeric class that doesn't
inherit from a core numeric type?  Wherever we draw the line, we need to
make it's well-documented.
>
> --
> ~Ethan~
>
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