[Python-Dev] PEP 498: Literal String Interpolation is ready for pronouncement

[Guido van Rossum]

On Sat, Sep 5, 2015 at 1:44 AM, haypo s <victor.stinner at gmail.com> wrote:

> 2015-09-05 5:01 GMT+02:00 Guido van Rossum <guido at python.org>:
> > And I'm ready to accept it. I'll wait until Tuesday night (Monday's a
> > holiday in the US) in case anything unforeseen comes up, but this is
> really
> > the Last Call for this PEP.
>
> String concatenation is inefficient in Python because strings are
> immutable. There is a micro-optimization which tried to reduce the bad
> performances of a+b, but it's better to avoid it.
>
> Python replaces >'abc' 'def'< with a single string >'abcdef'<. It's
> done by the parser, there is no overhead at runtime.
>
> PEP 498 allows to write >'abc' f'string'< which is replaced with
> >'abc' 'string'.__format__()< whereas str+str is a bad practice.
>
> I would prefer to force users to write an explicit '+' to remind them
> that there are more efficient ways to concatenate strings like
> ''.join((str1, str2)) or putting the first string in the f-string:
> >f'abcstring'<.
>
> Section in the PEP:
> https://www.python.org/dev/pepsstring/pep-0498/#concatenating-strings
>
> Victor
>

What does the extra + buy users? It's just more punctuation noise. The
implementation is intentionally left unspecified by the PEP; it should be
possible to design an implementation that combines all the parts together
more efficiently than the use of + (e.g. using a "string builder" object
internally).

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