[Python-Dev] PEP 461 Final?
ethan at stoneleaf.us
Sat Jan 18 02:51:05 CET 2014
On 01/17/2014 05:27 PM, Steven D'Aprano wrote:
> On Fri, Jan 17, 2014 at 08:49:21AM -0800, Ethan Furman wrote:
>> Overriding Principles
>> In order to avoid the problems of auto-conversion and Unicode
>> exceptions that could plague Py2 code, all object checking will
>> be done by duck-typing, not by values contained in a Unicode
>> representation _.
> I don't understand this paragraph. What does "values contained in a
> Unicode representation" mean?
Yeah, that is clunky. I'm trying to convey the idea that we don't want errors based on content, i.e. which characters
happens to be in a str.
>> %s is restricted in what it will accept::
>> - input type supports Py_buffer?
>> use it to collect the necessary bytes
> Can you give some examples of what types support Py_buffer? Presumably
> bytes. Anything else?
Anybody? Otherwise I'll go spelunking in the code.
>> - input type is something else?
>> use its __bytes__ method; if there isn't one, raise a TypeError
> I think you should explicitly state that this is a new special method,
> and state which built-in types will grow a __bytes__ method (if any).
It's not new. I know bytes, str, and numbers /do not/ have __bytes__.
>> 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.
As a quick thought experiment, why does "%d" % True return "1"?
>> Unsupported codes
>> %r (which calls __repr__), and %a (which calls ascii() on __repr__) are not
> +1 on not supporting b'%r' (i.e. I agree with the PEP).
> Why not support b'%a'? That seems to be a strange thing to prohibit.
I'll admit to being somewhat on the fence about %a.
It seems there are two possibilities with %a:
1) have it be ascii(repr(obj))
2) have it be str(obj).encode('ascii', 'strict')
(1) seems only useful for debugging, but even then not very -- if you switch from %s to %a you'll no longer see the
bytes output (although you would get the name of the object, which could be handy);
(2) is (slightly) blurring the lines between text and encoded-ascii; I would rather see "%s" % text.encode('ascii',
So we have two possibilities, both can be useful, I don't know which is most useful or even most logical.
So I guess I'm still open to arguments. :)
> Everythng else, well done and thank you.
You're welcome! Thank you to everyone who participated.
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