Evaluation of variable as f-string

[Johannes Bauer]

Am 27.01.23 um 20:18 schrieb Chris Angelico:

> All you tell us is
> what you're attempting to do, which there is *no good way to achieve*.

Fair enough, that is the answer. It's not possible.

>> Perhaps someone will be inspired to write a function to do it. 😎
> 
> See, we don't know what "it" is, so it's hard to write a function
> that's any better than the ones we've seen. Using eval() to construct
> an f-string and then parse it is TERRIBLE because:
> 
> 1) It still doesn't work in general, and thus has caveats like "you
> can't use this type of quote character"

Exactly my observation as well, which is why I was thinking there's 
something else I missed.

> 2) You would have to pass it a dictionary of variables, which also
> can't be done with full generality

Nonsense. I only am passing a SINGLE variable to eval, called "x". That 
is fully general.

> 3) These are the exact same problems, but backwards, that led to
> f-strings in the first place

I don't know what you mean by that.

> 4) eval is extremely slow and horrifically inefficient.

Let me worry about it.

> For some reason, str.format() isn't suitable,

I don't understand why you fully ignore literally the FIRST example I 
gave in my original post and angrily claim that you solution works when 
it does not:

x = { "y": "z" }
s = "-> {x['y']}"
print(s.format(x = x))
Traceback (most recent call last):
   File "<stdin>", line 1, in <module>
KeyError: "'y'"

This. Does. Not. Work.

I want to pass a single variable as a dictionary and access its members 
inside the expression.

>  but *you haven't said
> why*,

Yes I have, see above.

> Well, yes. If you asked "how can I do X", hoping the answer would be
> "with a runtime-evaluated f-string", then you're quite right - the
> answer might not be what you were hoping for. But since you asked "how
> can I evaluate a variable as if it were an f-string", the only
> possible answer is "you can't, and that's a horrible idea".

"You can't" would have been sufficient. Pity. Your judgement is 
unnecessary and, frankly, uncalled for as well. Multiple instances you 
claim that you have no idea what I am doing so how would you even begin 
to judge a solution as fit or unfit?

> Don't ask how to use X to do Y. Ask how to do Y.

You don't have to be angry that my question does not have a solution. I 
will manage and so might you.

Cheers,
Johannes