[Python-ideas] Briefer string format

Eric V. Smith eric at trueblade.com
Mon Jul 20 19:57:33 CEST 2015

On 07/20/2015 01:25 PM, Guido van Rossum wrote:
> Perhaps surprisingly, I find myself leaning in favor of the
> f'...{var}...' form. It is explicit in the variable name.
> Historically, the `x` notation as an alias for repr(x) was meant to play
> this role -- you'd write '...' + `var` + '...', but it wasn't brief
> enough, and the `` are hard to see. f'...' is more explicit, and can be
> combined with r'...' and b'...' (or both) as needed.

We didn't implement b''.format(), for a variety of reasons. Mostly to do
with user-defined types returning unicode from __format__, if I recall

So the idea is that
f'x:{a.x} y:{y}'
would translate to bytecode that does:
'x:{a.x} y:{y}'.format(a=a, y=y)


I think I could leverage _string.formatter_parser() to do this, although
it's been a while since I wrote that. And I'm not sure what's available
at compile time. But I can look into it.

I guess the other option is to have it generate:
'x:{a.x} y:{y}'.format_map(collections.ChainMap(globals(), locals(),

That way, I wouldn't have to parse the string to pick out what variables
are referenced in it, then have .format() parse it again.


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