[Python-Dev] PEP 461 Final?

[Ethan Furman]

On 01/19/2014 03:37 AM, Steven D'Aprano wrote:
> On Fri, Jan 17, 2014 at 05:51:05PM -0800, Ethan Furman wrote:
>> On 01/17/2014 05:27 PM, Steven D'Aprano wrote:
>
>>>> Numeric Format Codes
>>>> --------------------
>>>>
>>>> To properly handle int and float subclasses, int(), index(), and float()
>>>> will be called on the objects intended for (d, i, u), (b, o, x, X), and
>>>> (e, E, f, F, g, G).
>>>
>>>
>>> -1 on this idea.
>>>
>>> This is a rather large violation of the principle of least surprise, and
>>> radically different from the behaviour of Python 3 str. In Python 3,
>>> '%d' interpolation calls the __str__ method, so if you subclass, you can
>>> get the behaviour you want:
>>
>> Did you read the bug reports I linked to?  This behavior (which is a bug)
>> has already been fixed for Python3.4.
>
> No I didn't. This thread is huge, and it's only one of a number of huge
> threads about the same "bytes/unicode Python 2/3" stuff. I'm probably
> not the only person who missed the bug reports you linked to.

Fair point.


> If these bug reports are relevant to the PEP, you ought to list them in
> the PEP, and if they aren't relevant, I shan't be reading them *wink*

<mischievous grin>
Well, it seems to me they are more relevant to your misunderstanding of how %d and friends should work rather than to 
the PEP itself.  However, I suppose it possible you're not the only one so affected, so I'll link them in.
</mischeivous grin>


> In any case, whether I have succeeded in making the case against this
> aspect of the PEP or not

Not.  This was a bug that was fixed long before the PEP came into existence.


>> As a quick thought experiment, why does "%d" % True return "1"?
>
> I don't know. Perhaps it is a bug?

To summarize a rather long issue, %d and friends are /numeric/ codes; returning non-numeric text is inappropriate.  Yes, 
I realize there are other unicode values than also mean numeric digits, but they do not mean (so far as I know) Decimal 
digits, or Hexadecimal digits, or Octal digits.  (Obviously an ASCII slant going on there.)

Now that I've written that down, I think there are, in fact, other scripts that represent a base-10 number system with 
obviously different glyphs for the numbers....  Well, that means that this PEP just further strengthens the notion that 
format is for text (as then a custom numeric type could easily override the display even for :d, :h, etc.) and % is for 
bytes (where such glyphs are not natively representable anyway).

--
~Ethan~