[Python-Dev] PEP 461 Final? (original) (raw)

Ethan Furman ethan at stoneleaf.us
Mon Jan 20 07:15:24 CET 2014

On 01/19/2014 06:56 PM, Stephen J. Turnbull wrote:

Ethan Furman writes:

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). This argument is specious.

I don't think so. I think it's a good argument for the future of Python code. Mind you, I should probably have said % is primarily for bytes, or even more useful for bytes than for text. The idea being that true text fun stuff requires format, while bytes can only use % for easy formatting.

Alternative numeric characters [are] just as representable as the ASCII digits are, and in the same way (by defining a bytes <-> str mapping, aka codec). The problem is not that they're non-representable, it's that they're non-ASCII, and the numeric format codes implicitly specify the ASCII numerals when in text as well as when in bytes.

Certainly. And you can't change that either. Oh, wait, you can! Define your own!

 class LocalNum(int):
     "displays d, i, and u codes in local language"

     def __format__(self, fmt):
         # do the fancy stuff so the characters are not ASCII, but whatever
         # is local here

Then you could have your text /and/ your numbers be in your own language. But you can't get that using % unless you always call a custom function and use %s.

(Note that "'{:d}'.format(True)" -> '1' works because True is an int and so can be d-formatted in principle. It's not an exceptional case. It's a different issue from what you're talking about here.)

"'{:d}'.format(True)" is not exceptional, you're right. But "'%d' % True" is, and was singled-out in the unicode display code to print as '1' and not as 'True'. (Now all int subclasses behave this way (in 3.4 anyways).)

And I think it's the same issue, or at least closely related. If you create a custom number type with the intention of displaying them in the local lingo, you have to use format because % is hard coded to yield digits that map to ASCII.

These PEPs provide a crutch for such crippled software, allowing them to hobble into the House of Python 3.

Very picturesque.

That's obvious, so please don't try to obfuscate it; just declare "consenting adults" and move on.

Lots of features can be abused. That doesn't mean we shouldn't talk about the intended use cases and encourage those.

-- Ethan

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