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~
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