[Python-ideas] Briefer string format

[Eric V. Smith]

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.