[Python-ideas] Briefer string format

[Guido van Rossum]

On Fri, Jul 24, 2015 at 10:27 PM, Ben Finney <ben+python at benfinney.id.au>
wrote:

> Greg Ewing <greg.ewing at canterbury.ac.nz> writes:
>
> > Steven D'Aprano wrote:
> >
> > > I don't think I want this behaviour:
> > >
> > >     f'{spam}' '{eggs}'
> > >     => format(spam) + '{eggs}'
> >
> > What do you think should happen in this case:
> >
> >    '{spam}' f'{eggs}'
> >
> > It would seem very strange to me if the f infected strings *before* it
> > as well as after it.
>
> The existing behaviour of implicit concatenation doesn't give much of a
> guide here, unfortunately::
>
>     >>> 'foo\abar' r'lorem\tipsum' 'wibble\bwobble'
>     'foo\x07barlorem\\tipsumwibble\x08wobble'
>
>     >>> type(b'abc' 'def' b'ghi')
>       File "<stdin>", line 1
>     SyntaxError: cannot mix bytes and nonbytes literals
>
> So, the ‘b’ prefix expects to apply to all the implicitly-concatenated
> parts (and fails if they're not all bytes strings); the ‘r’ prefix
> expects to apply only to the one fragment, leaving others alone.
>
> Is the proposed ‘f’ prefix, on a fragment in implicit concatenation,
> meant to have behaviour analogous to the ‘r’ prefix or the ‘b’ prefix,
> or something else? What's the argument in favour of that choice?
>

It *must* work like r'' does. Implicit concatenation must be thought of as
letting each string do its thing and then concatenating using '+', just
optimized if possible. The error for b'' comes out because the '+' refuses
b'' + ''.

I find it a sign of the times that even this simple argument goes on and on
forever. Please stop the thread until Eric has had the time to write up a
PEP.

-- 
--Guido van Rossum (python.org/~guido)
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