[Python-ideas] Briefer string format

[Stefan Behnel]

Mike Miller schrieb am 20.07.2015 um 01:35:
>     csstext += '{nl}{key}{space}{{{nl}'.format(**locals())
> 
> This looks a bit better if you ignore the right half, but it is longer and not
> as simple as one might hope.  It is much longer still if you type out the
> variables needed as kewword params!  The '{}' option is not much improvement
> either.
> 
>    csstext += '{nl}{key}{space}{{{nl}'.format(nl=nl, key=key, ...  # uggh
>    csstext += '{}{}{}{{{}'.format(nl, key, space, nl)
> 
> I've long wished python could format strings easily like bash or perl do, ...
> and then it hit me:
> 
>     csstext += f'{nl}{key}{space}{{{nl}'
> 
> An "f-formatted" string could automatically format with the locals dict. Not
> yet sure about globals, and unicode only suggested for now.  Perhaps could be
> done directly to avoid the .format() function call, which adds some overhead
> and tends to double the length of the line?

Is this an actual use case that people *commonly* run into? I understand
that the implicit name lookups here are safe and all that, but I cannot
recall ever actually using locals() for string formatting.

The above looks magical to me. It's completely unclear that string
interpolation is happening behind my back here, unless I already know it. I
think it's ok to have a "b" string prefix produce a special kind of string
and expect people to guess that and look up what it does if they don't know
(and syntax like a string prefix is difficult enough to look up already).
Having an "f" prefix interpolate the string with names from the current
namespace is way beyond what I would expect a string prefix to do.

I'd prefer not seeing a "cool feature" added just "because it's cool". If
it additionally is magic, it's usually not a good idea.

Stefan