On Thu, 24 Jun 2021 at 17:25, Eric Nieuwland <[email protected]> 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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