| ▲ | jackpirate 9 days ago |
| Building off this question, it's not clear to me why Python should have both t-strings and f-strings. The difference between the two seems like a stumbling block to new programmers, and my "ideal python" would have only one of these mechanisms. |
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| ▲ | nhumrich 9 days ago | parent | next [-] |
| f-strings immediately become a string, and are "invisible" to the runtime from a normal string. t-strings introduce an object so that libraries can do custom logic/formatting on the template strings, such as decided _how_ to format the string. My main motivation as an author of 501 was to ensure user input is properly escaped when inserting into sql, which you cant enforce with f-strings. |
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| ▲ | williamdclt 9 days ago | parent | next [-] | | > ensure user input is properly escaped when inserting into sql I used to wish for that and got it in JS with template strings and libs around it. For what it’s worth (you got a whole PEP done, you have more credibility than I do) I ended up changing my mind, I think it’s a mistake. It’s _nice_ from a syntax perspective. But it obscures the reality of sql query/parameter segregation, it builds an abstraction on top of sql that’s leaky and doesn’t even look like an abstraction. And more importantly, it looks _way too close_ to the wrong thing. If the difference between the safe way to do sql and the unsafe way is one character and a non-trivial understanding of string formatting in python… bad things will happen. In a one-person project it’s manageable, in a bigger one where people have different experiences and seniority it will go wrong. It’s certainly cute. I don’t thing it’s a good thing for sql queries. | | |
| ▲ | nine_k 9 days ago | parent [-] | | I understand your concern, and I think the PEP addresses it. Quite bluntly, t"foo" is not a string, while f"foo" is. You'll get a typecheck error if you run a typechecker like any reasonable developer, and will get a runtime error if you ignore the type mismatch, because t"foo" even lacks a __str__() method. One statement the PEP could put front and center in the abstract could be "t-strings are not strings". | | |
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| ▲ | jackpirate 8 days ago | parent | prev [-] | | That all make senses to me. But it definitely won't make sense to my intro to programming students. They already have enough weird syntax to juggle. | | |
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| ▲ | davepeck 9 days ago | parent | prev | next [-] |
| For one thing, `f"something"` is of type `str`; `t"something"` is of type `string.templatelib.Template`. With t-strings, your code can know which parts of the string were dynamically substituted and which were not. |
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| ▲ | all2 9 days ago | parent | next [-] | | The types aren't so important. __call__ or reference returns type string, an f and a t will be interchangeable from the consumer side. Example, if you can go through (I'm not sure you can) and trivially replace all your fs with ts, and then have some minor fixups where the final product is used, I don't think a migration from one to the other would be terribly painful. Time-consuming, yes. | | | |
| ▲ | 9 days ago | parent | prev [-] | | [deleted] |
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| ▲ | skeledrew 9 days ago | parent | prev [-] |
| Give it a few years to when f-string usage has worn off to the point that a decision can be made to remove it without breaking a significant number of projects in the wild. |
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| ▲ | milesrout 9 days ago | parent | next [-] | | That will never happen. | | |
| ▲ | skeledrew 9 days ago | parent | next [-] | | Well if it continues to be popular then that is all good. Just keep it. What matters is that usage isn't complex for anyone. | | |
| ▲ | macNchz 9 days ago | parent [-] | | Well now we'll have four different ways to format strings, since removing old ones is something that doesn't actually happen: "foo %s" % "bar"
"foo {}".format("bar")
bar = "bar"; f"foo {bar}"
bar = "bar"; t"foo {bar}" # has extra functionality!
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| ▲ | amenghra 9 days ago | parent | next [-] | | This is where an opinionated linter comes in handy. Ensures people gradually move to the “better” version while not breaking backwards compatibility. It does suck for beginners who end up having to know about all variations until their usage drops off. | | |
| ▲ | QuercusMax 9 days ago | parent [-] | | The linter is a big deal, actually. I've worked with Python off and on during the past few decades; I just recently moved onto a project that uses Python with a bunch of linters and autoformatters enabled. I was used to writing my strings ('foo %s % bar), and the precommit linter told me to write f'foo %{bar}'. Easy enough! |
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| ▲ | rtpg 9 days ago | parent | prev | next [-] | | printf-style formatting ("foo %s" % "bar") feels the most ready to be retired (except insofar as it probably never will, because it's a nice shortcut). The other ones at least are based on the same format string syntax. "foo {}".format("bar") would be an obvious "just use f-string" case, except when the formatting happens far off. But in that case you could "just" use t-strings? Except in cases where you're (for example) reading a format string from a file. Remember, t- and f- strings are syntactic elements, so dynamism prevents usage of it! So you have the following use cases: - printf-style formatting: some C-style string formatting is needed - .format: You can't use an f- string because of non-locality in data to format, and you can't use a t- string due to dynamism in - f-string: you have the template and the data in the same spot lexicographically, and you just want string concatenation (very common!) - t-string: you have the template and the data in the same spot lexicogrpahically, but want to use special logic to actually build up your resulting value (which might not even be a string!) The last two additions being syntax makes it hard to use them to cover all use cases of the first two. But in a specific use case? It's very likely that there is an exact best answer amongst these 4. | | |
| ▲ | masklinn 8 days ago | parent | next [-] | | > printf-style formatting ("foo %s" % "bar") feels the most ready to be retired (except insofar as it probably never will, because it's a nice shortcut). It’s also the only one which is anything near safe for being user provided. | | |
| ▲ | pansa2 8 days ago | parent | next [-] | | I don’t think I’ve ever used % formatting in Python - what makes it safer than `format`? | | |
| ▲ | masklinn 8 days ago | parent [-] | | `str.format` allows the format string to navigate through indexes, entries, and attributes. If the result of the formatting is echoed back and any non-trivial object it passed in, it allows for all sorts of introspection. printf-style... does not support any of that. It can only format the objects passed in. |
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| ▲ | rtpg 7 days ago | parent | prev [-] | | Very good point. While I think we could do away with the syntactic shorthand, definitely would want to keep some function/method around with the capabilities. |
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| ▲ | milesrout 8 days ago | parent | prev [-] | | .format is also nice because you can have more complex subexpressions broken over multiple lines instead of having complex expressions inside the {}. |
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| ▲ | skeledrew 9 days ago | parent | prev | next [-] | | And if it's being used, and isn't considered problematic, then it should remain. I've found use for all the current ones:
(1) for text that naturally has curlies,
(2) for templating
(3) for immediate interpolation, and improved at-site readability I see (4) being about the flexibility of (2) and readability of (3). Maybe it'll eventually grow to dominate one or both, but it's also fine if it doesn't. I don't see (1) going away at all since the curly collision still exists in (4). | |
| ▲ | milesrout 8 days ago | parent | prev | next [-] | | Don't forget string.Template: import string
t = string.Template("foo $bar")
t.substitute(bar="bar")
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| ▲ | darthrupert 8 days ago | parent | prev [-] | | Five, if you count the log module. I hope t-strings will come there soon. log.error("foo happend %s", reason) |
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| ▲ | bcoates 8 days ago | parent | prev [-] | | Putting down my marker on the opposite. Once you're targeting a version of python that has t-strings, decent linters/libraries have an excuse to put almost all uses of f-strings in the ground. |
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| ▲ | aatd86 9 days ago | parent | prev [-] | | No backward compatibility?! | | |
| ▲ | skeledrew 9 days ago | parent [-] | | If the usage of a feature is significantly close enough to 0 because there is a well used alternative, what need is there for backward compatibility? If anything, it can be pushed to a third party package on PyPI. |
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