[Python-ideas] Briefer string format

[Eric V. Smith]

On 08/01/2015 02:07 PM, Steve Dower wrote:
> +1 for !r/!s and not being arbitrarily incompatible with existing
> formatting. (I also really like being able to align string literals
> using an f-string. That seems to come up all the time in my shorter
> scripts for headings etc.)

I meant to write that last example as:
>>> f'{"foo"!r:10}'
"'foo'     "

You can of course mix !r with a string format specifier.

Eric.

> Cheers,
> Steve
> 
> Top-posted from my Windows Phone
> ------------------------------------------------------------------------
> From: Eric V. Smith <mailto:eric at trueblade.com>
> Sent: ‎8/‎1/‎2015 10:44
> To: python-ideas at python.org <mailto:python-ideas at python.org>
> Subject: Re: [Python-ideas] Briefer string format
> 
> On 7/25/2015 3:55 PM, Eric V. Smith wrote:
>> In trying to understand the issues for a PEP, I'm working on a sample
>> implementation. There, I've just disallowed concatentation entirely.
>> Compared to all of the other issues, it's really insignificant. I'll put
>> it back at some point.
> 
> I'm basically done with my implementation of f-strings.
> 
> I really can't decide if I want to allow adjacent f-string concatenation
> or not. I'm leaning towards not. I don't like mixing compile-time
> concatenation with run-time expression evaluation. But my mind is not
> made up.
> 
> One issue that has cropped up:
> 
> Should we support !s and !r, like str.format does? It's not really
> needed, since with f-strings you can just call str or repr yourself:
> 
>>>> f'{"foo":10}'
> 'foo       '
>>>> f'{repr("foo"):10}'
> "'foo'     "
> 
> Do we also need to support:
> 
>>>> f'{"foo"!r}'
> "'foo'"
> 
> With str.format, !s and !r are needed because you can't put the call to
> repr in str.format's very limited expression syntax. But since f-strings
> support arbitrary expressions, it's not needed. Still, I'm leaning
> toward including it for two reasons: it's concise, and there's no reason
> to be arbitrarily incompatible with str.format. If I include !s and !r,
> then the only way that str.format differs from f-string expressions is
> in non-numeric subscripting (unfortunate, but discussed previously and I
> think required). This ignores the fact that f-string expressions
> encompass all Python expressions, while str.format is extremely limited.
> 
> I'll start working on the PEP shortly.
> 
> Eric.
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