I didn’t make myself clear, sorry.
The code example was just to give an initial what I was suggesting.
The errors you show demonstrate the example is incomplete.
I’d like them to work.
> On 24 Jun 2021, at 18:37, Martin (gzlist) <gzl...@googlemail.com> wrote:
>
> On Thu, 24 Jun 2021 at 17:25, Eric Nieuwland <eric.nieuwl...@gmail.com> wrote:
>>
>> class DelayedFString(str):
>> def __str__(self):
>> vars = inspect.currentframe().f_back.f_globals.copy()
>> vars.update(inspect.currentframe().f_back.f_locals)
>> return self.format(**vars)
>
> This isn't quite right as the semantics between f-strings and
> str.format() are not actually the same (though this isn't well
> documented):
>
>>>> f'{1 + 2}'
> '3'
>>>> str(DelayedFString('{1 + 2}'))
> Traceback (most recent call last):
> File "<stdin>", line 1, in <module>
> File "<stdin>", line 5, in __str__
> KeyError: '1 + 2'
>
>>>> d = dict(a=1)
>>>> f'{d["a"]}'
> '1'
>>>> str(DelayedFString('{d["a"]}'))
> Traceback (most recent call last):
> File "<stdin>", line 1, in <module>
> File "<stdin>", line 5, in __str__
> KeyError: '"a"'
>
> Basically, f-strings rely on eval-like semantics.
>
> Martin
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