On Sat, 28 Jan 2023 at 05:31, Rob Cliffe via Python-list <python-list@python.org> wrote: > On 23/01/2023 18:02, Chris Angelico wrote: > > Maybe, rather than asking for a way to treat a string as code, ask for > > what you ACTUALLY need, and we can help? > > > > ChrisA > Fair enough, Chris, but still ISTM that it is reasonable to ask (perhaps > for a different use-case) whether there is a way of evaluating a string > at runtime as if it were an f-string. We encourage people to ask > questions on this list, even though the answer will not always be what > they're hoping for.
No, it's not, because that's the "how do I use X to do Y" problem. Instead, just ask how to do *what you actually need*. If the best way to do that is to eval an f-string, then someone will suggest that. But, much much much more likely, the best way to do it would be something completely different. What, exactly? That's hard to say, because *we don't know what you actually need*. All you tell us is what you're attempting to do, which there is *no good way to achieve*. > I appreciate that the answer may be "No, because it would be a lot of > work - and increase the maintenance burden - to support a relatively > rare requirement". What about: "No, because it's a terrible TERRIBLE idea, requires that you do things horribly backwards, and we still don't even know what you're trying to do"? > 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" 2) You would have to pass it a dictionary of variables, which also can't be done with full generality 3) These are the exact same problems, but backwards, that led to f-strings in the first place 4) eval is extremely slow and horrifically inefficient. For some reason, str.format() isn't suitable, but *you haven't said why*, so we have to avoid that in our solutions. So, to come back to your concern: > We encourage people to ask > questions on this list, even though the answer will not always be what > they're hoping for. 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". Don't ask how to use X to do Y. Ask how to do Y. ChrisA -- https://mail.python.org/mailman/listinfo/python-list
