[Python-Dev] PEP-498: Literal String Formatting

Nick Coghlan ncoghlan at gmail.com
Sat Aug 8 11:34:57 CEST 2015

On 8 August 2015 at 11:39, Eric V. Smith <eric at trueblade.com> wrote:
> Following a long discussion on python-ideas, I've posted my draft of
> PEP-498. It describes the "f-string" approach that was the subject of
> the "Briefer string format" thread. I'm open to a better title than
> "Literal String Formatting".

Thanks you for your work on this - it's a very cool concept!

I've also now written and posted an initial draft of PEP 500, based
directly on PEP 498, which formalises the "__interpolate__" builtin
idea I raised in those threads, along with a PEP 292 based syntax
proposal that aims to be as simple as possible for the simple case of
interpolating existing variables, while still allowing the use of
braces to permit embedding of arbitrary expressions and formatting

it turned out this approach provided an unanticipated benefit that I
only discovered while writing the PEP: by defining a separate
"__interpolateb__" builtin, it's straightforward to define binary
interpolation in terms of bytes.__mod__, while still defining text
interpolation in terms of str.format.

The previously-redundant-in-python-3 'u' prefix also finds new life as
a way of always requesting the default string interpolation, even if
__interpolate__ has been overridden in the current namespace to mean
something else (like il8n string translation).


Nick Coghlan   |   ncoghlan at gmail.com   |   Brisbane, Australia

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