> In addition, I hope that the tooling ecosystem will adapt to support t-strings. For instance, I’d love to see black and ruff format t-string contents, and vscode color those contents, if they’re a common type like HTML or SQL.
This is such a strange take on t-strings. The only way for anything to infer that the template string is supposed to turn into valid HTML or SQL is to base it of the apparent syntax in the string, which can only be done in an ad-hoc fashion and has nothing to do with the template string feature.
The way the feature has been designed there is no indication in the string itself what type of content it is or what it will eventually be converted to. It’s all handled by the converting function.
As others have added, something like sql”select * from {table}” would have been able to do this, but there’s not even any guarantees that something that is in a template that will be converted into valid sql by a converting function should be any type of valid sql prior to that conversion. For all you know t“give me {table} but only {columns}” might be a converted into valid sql after the template is processed.
As Paul mentioned, we spent quite a lot of time considering these issues as PEP 750 came together. In the end, we concluded (a) the PEP leaves open quite a few potential approaches for tools to adopt (not just the one you suggest, as others here have pointed out), and (b) it's ultimately something that the broader tooling community needs to rally around and should probably be out of scope for the PEP itself.
But without having that background, it might indeed seem strange that I am hopeful we'll see the ecosystem adapt! :-)
The original PEP and the original discussion had this in scope. We removed it to let this emerge later. There are different ways to signal the language -- some more friendly to tooling, some more robust.
And highlighters and static analyzers will key off of this.
JavaScript's tagged template literals are actually about as flexible as this, since you can dynamically choose the tag function, it's just very rare to do so, so tools assume a lot based on the name of the function. Python tools can basically do the same thing, and just not support t-strings that aren't nested inside a well-named processing function.
> The only way for anything to infer that the template string is supposed to turn into valid HTML or SQL is to base it of the apparent syntax in the string
Not the only thing. You can also look at how it is used. Your editor could know of how some popular libraries use t-strings, track which t-strings get passed into functions from those libraries, and use that to assume what grammar the t-string should follow.
Is that cheating? In some sense, yes, but it also is useful and likely will be worth it for quite a few programmers.
Couldn’t you do this with a type annotation? e.g. SQLAlchemy could have a SQL type so tools like mypy could see a Template instance and confirm you’re using it safely but Black, Ruff, or SQLFluff could look for the more specialized Annotated[Template, SQL] to realize that the template could be formatted as SQL, and something like Django could even have Annotated[Template, Email], Annotated[Template, HTML], or Annotated[Template, JSX] to indicate what context the same templating syntax is targeting.
This is what we discussed in the first revision of the PEP (the use of `Annotated`.) But we found out: linters don't know anything about the Python type system.
We hope to get a community around all of this, stuff at PyCon US, EuroPython, etc. and work some of this out. The JSX/TSX world really has good tooling. We can provide that for those that want it, perhaps better on some aspects.
Note that the variables are safely and correctly interpolated at compile time. And it's type checked across the boundary too, by checking (at compile time) the column types with the live database.
Yes, what you did is strictly more powerful than what the Python people did. And you did it 20 years ago. Well done, have an upvote. And yet, here we are in 2025 with Python popularity growing unstoppably and (approximately) no one caring about OCaml (and all the other languages better than Python). It makes me sad.
It's interesting how the majority has explicitly chosen NOT to use the "better" languages. Is the majority really that bad in their judgment? Or is it that "better" is actually defined by adoption over time?
But my two cents is that we're pretty lucky it's python that has taken off like a rocket. It's not my favorite language, but there are far worse that it could have been.
I'm switching between C, OCaml, Python, bash & Rust roughly equally every day (to a lesser extent, Perl as well). Not everything is what gets on the front page of HN.
Aren't there other benefits to server-side parameter binding besides just SQL-injection safety? For instance, using PG's extended protocol (binary) instead of just raw SQL strings. Caching parameterized prepared statements, etc.
Also:
db.execute(t"QUERY WHERE name = {name}")
Is dangerously close to:
db.execute(f"QUERY WHERE name = {name}")
A single character difference and now you've just made yourself trivially injectible.
I don't think this new format specifier is in any way applicable to SQL queries.
Templates are a very different duck type from strings and intentionally don't support __str__(). The SQL tool can provide a `safe_execute(Template)` that throws if passed a string and not a Template. You can imagine future libraries that only support Template and drop all functions that accept strings as truly safe query libraries.
> Caching parameterized prepared statements, etc.
Templates give you all the data you need to also build things like cacheable parameterized prepared statements. For DB engines that support named parameters you can even get the interpolation expression to auto-name parameters (get the string "name" from your example as the name of the variable filling the slot) for additional debugging/sometimes caching benefits.
> Aren't there other benefits to server-side parameter binding besides just SQL-injection safety? For instance, using PG's extended protocol (binary) instead of just raw SQL strings. Caching parameterized prepared statements, etc.
All of which can be implemented on top of template strings.
> A single character difference and now you've just made yourself trivially injectible.
It's not just a one character difference, it's a different type. So `db.execute` can reject strings both statically and dynamically.
> I don't think
Definitely true.
> this new format specifier is in any way applicable to SQL queries.
The first mistake we're going to see a library developer make is:
def execute(query: Union[str, Template]):
Maybe because they want their execute function to be backwards compatible, or just because they really do want to allow either raw strings are a template string.
> they really do want to allow either raw strings are a template string.
I’d consider that an invalid use case:
1. You can create a template string without placeholders.
2. Even if the caller does need to pass in a string (because they’re executing from a file, or t-strings don’t support e.g. facetting) then they can just… wrap the string in a template explicitly.
You solve that with an execute(stmt) function that requires you to pass in a template.
In Javascript, sql`where id = ${id}` is dangerously close to normal string interpolation `where id = ${id}`, and db libs that offer a sql tag have query(stmt) fns that reject strings.
This is true of many other things, which is why we have type checkers and linters to be perfectly rigorous rather than expecting humans to never make mistakes.
Because they're both passed to "execute", which can't tell between the f-string and a non-interpolated query, so it just has to trust you did the right thing. Typoing the "t" as an "f" introduces SQL injection that's hard to spot.
Assuming `execute` takes both. You could have `execute(template)` and `execute_interpolated(str, ...args)` but yeah if it takes both you'll have challenges discouraging plain-text interpolation.
It would have to be the other way around or be a (possibly major) breaking change. Just execute() with strings is already standard python that all the frameworks build on top of, not to mention tutorials:
With t-strings you could run proper escaping over the contents of `some_file` before passing it to a shell.
I'd have to take a look at the order things happen in shell, but you might even be able to increase security/foot-gun-potential a little bit here by turning this into something like `stat "$( base64 -d [base64 encoded content of some_file] )"`.
Python is not the first one to get this feature. It's been present in JS for some time now, and before that in C# (not sure if that's the origin or they also borrowed it from somewhere). Python adopted it based in part on successful experience in those other languages.
The key point is that t-strings are not strings. Db.execute(t”…”) would throw an exception, because t”…” is not a string and cannot be interpreted as one.
In order for a library to accept t-strings, they need to make a new function. Or else change the behavior and method signature of an old function, which I guess they could do but any sanely designed library doesn’t do.
Handling t-strings will require new functions to be added to libraries.
> The problem is writing f instead of t => and this will silently work I assume (not a Python dev just trying to understand the language design)
In the fullness of time it has no reason to. Even in the worst case scenario where you have to compose the query dynamically in a way t-strings can’t support, you can just instantiate a Template object explicitely.
The execute function can recognize it as a t-string and prevent SQL injection if the name is coming from user input. f-strings immediately evaluate to a string, whereas t-strings evaluate to a template object which requires further processing to turn it into a string.
Then the useful part is the extra execute function you have to write (it's not just a substitute like in the comment) and an extra function can confirm the safety of a value going into a f-string just as well.
I get the general case, but even then it seems like an implicit anti-pattern over doing db.execute(f"QUERY WHERE name = {safe(name)}")
Problem with that example is where do you get `safe`? Passing a template into `db.execute` lets the `db` instance handle safety specifically for the backend it's connected to. Otherwise, you'd need to create a `safe` function with a db connection to properly sanitize a string.
And further, if `safe` just returns a string, you still lose out on the ability for `db.execute` to pass the parameter a different way -- you've lost the information that a variable is being interpolated into the string.
db.safe same as the new db.execute with safety checks in it you create for the t-string but yes I can see some benefits (though I'm still not a fan for my own codebases so far) with using the values further or more complex cases than this.
Yeah but it would have to be something like `db.safe("SELECT * FROM table WHERE id = {}", row_id)` instead of `db.execute(t"SELECT * FROM table WHERE id = {row_id}")`.
This is just extra boilerplate though, for what purpose?.
I think one thing you might be missing is that in the t-string version, `db.execute` is not taking a string; a t-string resolves to an object of a particular type. So it is doing your `db.safe` operation, but automatically.
Of course you can write code like that. This is about making it easier not to accidentally cause code injection by forgetting the call of safe(). JavaScript had the same feature and some SQL libraries allow only the passing of template strings, not normal strings, so you can't generate a string with code injection. If you have to dynamically generate queries they allow that a parameter is another template string and then those are merged correctly. It's about reducing the likelihood of making mistakes with fewer key strokes. We could all just write untyped assembly instead and could do it safely by paying really good attention.
agreed. but then you're breaking the existing `db.execute(str)`. if you don't do that, and instead add `db.safe_execute(tpl: Template)`, then you're back to the risk that a user can forget to call the safe function.
also, you're trusting that the library implementer raises a runtime exception if a string a passed where a template is expected. it's not enough to rely on type-checks/linting. and there is probably going to be a temptation to accept `db.execute(sql: Union[str, Template])` because this is non-breaking, and sql without params doesn't need to be templated - so it's breaking some stuff that doesn't need to be broken.
i'm not saying templates aren't a good step forward, just that they're also susceptible to the same problems we have now if not used correctly.
> and an extra function can confirm the safety of a value going into a f-string just as well.
Yes, you could require consumers to explicitly sanitize each parameter before it goes into the f-string, or, because it has the structure of what is fixed and what is parameters, it can do all of that for all parameters when it gets a t-string.
The latter is far more reliable, and you can't do it with an f-string because an f-string after creation is just a static string with no information about construction.
Some SQL engines support accepting parameters separately so that values get bound to the query once the abstract syntax tree is already built, which is way safer than string escapes shenanigans.
I’d always prefer to use a prepared statement if I can, but sadly that’s also less feasible in the fancy new serverless execution environments where the DB adapter often can’t support them.
For me it just makes it easier to identify as safe, because it might not be obvious at a glance that an interpolated template string is properly sanitised.
Your "old" db.execute (which presumably accepts a regular old string) would not accept a t-string, because it's not a string. In the original example, it's a new db.execute.
Using a t-string in a db.execute which is not compatible with t-strings will result in an error.
Using a t-string in a db-execute which is, should be as safe as using external parameters. And using a non-t-string in that context should (eventually) be rejected.
Yes, but if a function accepts a template (which is a different type of object from a string!), either it is doing sanitization, or it explicitly implemented template support without doing sanitization—hard to do by accident!
The key point here is that a "t-string" isn't a string at all, it's a new kind of literal that's reusing string syntax to create Template objects. That's what makes this new feature fundamentally different from f-strings. Since it's a new type of object, libraries that accept strings will either have to handle it explicitly or raise a TypeError at runtime.
I'm not sure why you think it's harder to use them without sanitization - there is nothing inherent about checking the value in it, it's just a nice use.
You might have implemented the t-string to save the value or log it better or something and not even have thought to check or escape anything and definitely not everything (just how people forget to do that elsewhere).
I really think you're misunderstanding the feature. If a method has a signature like:
class DB:
def execute(query: Template):
...
It would be weird for the implementation to just concatenate everything in the template together into a string without doing any processing of the template parameters. If you wanted an unprocessed string, you would just have the parameter be a string.
I'm not. Again, you might be processing the variable for logging or saving or passing elsewhere as well or many other reasons unrelated to sanitization.
Taking a Template parameter into a database library's `execute` method is a big bright billboard level hint that the method is going to process the template parameters with the intent to make the query safe. The documentation will also describe the behavior.
You're right that the authors of such libraries could choose to do something different with the template parameter. But none of them will, for normal interface design reasons.
A library author could also write an implementation of a `plus` function on a numerical type that takes another numerical type, and return a string with the two numbers concatenated, rather than adding them together.
But nobody will do that, because libraries with extremely surprising behavior like that won't get used by anybody, and library authors don't want to write useless libraries. This is the same.
It's true that in theory `db.execute` could ignore semantics and concatenate together the template and variables to make a string without doing any sanitisation, but isn't the same true of the syntax it was claimed to replace?
Just because templates (or the previous syntax of passing in variables separately) could be used in a way that's equivalent (safety-wise) to an f-string by a poorly designed library does not mean that they add nothing over an f-string in general - they move the interpolation into db.execute where it can do its own sanitization and, realistically, sqlite3 and other libraries explicitly updated to take these will do proper sanitization.
Assuming you also need to format non-values in the SQL (e.g. column names), how does the `execute` function is supposed to make the difference between stuff that should be formatted in the string vs a parametrized value?
However I think using the format spec that way would be dubious and risky, because it makes the sink responsible for whitelisting values, and that means any processing between the source and sink becomes a major risk. It's the same issue as HTML templates providing `raw` output, now you have to know to audit any modification to the upstream values which end there, which is a lot harder to do than when "raw markup" values are reified.
> rather than with some "out-of-band" logic.
It's the opposite, moving it to the format spec is out of band because it's not attached to values, it just says "whatever value is here is safe", which is generally not true.
Unless you use the format spec as a way to signal that a term should use identifier escaping rules rather than value escaping rules (something only the sink knows), and an `Identifier` wrapper remains a way to bypass that.
> Unless you use the format spec as a way to signal that a term should use identifier escaping rules rather than value escaping rules (something only the sink knows)
This should be quiet common in the SQL applications. It will be nice to write t"select {name:id} from {table:id} where age={age}" and be confident that the SQL will be formatted correctly, with interpolations defaulting to (safe) literal values.
The article does mention that the function receiving the template has access to those formatting options for each interpolation, so presumably you could abuse the ones that are available for that purpose?
I think it's just giving an error because a valid AST can't be made, which means valid bytecode can't be made. "<word> <word>" is only valid syntax if one is a reserved word. `nonlocal(foo)` is just fine, of course.
Now instead of being explicit all it takes is someone unfamiliar with t strings (which will be almost everyone - still few know about f strings and their formatting capabilities) to use an f instead and you are in for a bad time.
Any sane library will just error when you pass a string to a function that expects a template though. And that library will have types too so your IDE tells you before you get that far.
Such library functions tend to also accept a string as a valid input. E.g. db.execute from the GP usually works with strings to allow non-parametrized SQL queries.
A library can extend an existing database library like 'pg' so that PgClient#query() and PgPool#query() require string template statements.
That way 'pg' can continue working with strings, and people who want nice templated strings can use the small extension library, and the small extension library makes it impossible to accidentally pass strings into the query functions.
I suppose lack of overlap in the "interface surface" (attributes, including callables) between `str` and `Template` should nip the kind of issue in the bud -- being passed a `Template` and needing to actually "instantiate" it -- accessing `strings` and `values` attributes on the passed object, will likely fail at runtime when attempted on a string someone passed instead (e.g. confusing a `t`-string with an `f`-string)?
That is an issue, but essentially it boils down to the existing risk of unknowledgeable people not escaping untrusted inputs. The solution should be more education and better tooling (linters, SAST), and t-strings are likely to help with both.
Landing in 3.14? Nice, but also oof, that's probably not getting to my employer's codebase for a year or two. And it sounds like it could really solve some problems for us, too.
Paging asottile - any plans to make a `future-tstrings`? :)
Will this allow neat SQL syntax like the following?
city = 'London'
min_age = 21
# Find all users in London who are 21 or older:
users = db.get(t'
SELECT * FROM users
WHERE city={city} AND age>{min_age}
')
If the db.get() function accepts a template, it should, right?
This would be the nicest way to use SQL I have seen yet.
Isn't the actually proper way to use prepared statements anyway? If we are doing that properly, then what does this t string business buy us for SQL usage from Python?
Except to maintain backwards compatibility we're probably going to get new methods that only accept templates, completely circumventing any effort to stop people passing in strings.
Prepared statements were the recommended way to run SQL queries when I was starting with PHP 15 years ago, anyone writing code vulnerable to SQL injection at this point should not be writing code.
That’s the sort of thing people have built with the equivalent feature in JavaScript, so it should do. Eg https://github.com/andywer/squid is a nice example.
Thanks, I hate it. While it's nice syntactic sugar, the difference between an SQL injection vulnerability and a properly parametrized query is now a single letter that's easily missed
The t-string produces a Template object without a __str__() method. You can’t mistakenly use an f-string in its place. Either the code expects a string, in which case passing it a Template would blow it up, or the code expects a Template, in which case passing it a string would blow it up.
> or the code expects a Template, in which case passing it a string would blow it up.
That's where the problem is though -- in most cases it probably won't blow up.
Plenty of SQL queries don't have any parameters at all. You're just getting the number of rows in a table or something. A raw string is perfectly fine.
Will sqlite3 really disallow strings? Will it force you to use templates, even when the template doesn't contain any parameters?
You can argue it should, but that's not being very friendly with inputs, and will break backwards compatibility. Maybe if there's a flag you can set in the module to enable that strict behavior though, with the idea that in a decade it will become the default?
It's one extra letter to "force" for an unparameterized query over a "raw string". The t-string itself works just fine without parameters.
There's definitely a backwards compatibility hurdle of switching to a template-only API, but a template-only API doesn't look that much "less friendly" with inputs, when the only difference is a `t` before every string, regardless of number of parameters.
Sure, but it's just I don't have to do that anywhere else.
I never put an f in front of a string if I'm not putting variables within it.
And I'm generally used to Python inputs being liberal. I can usually pass a list if it expects a tuple; I can pass an int if it expects a float; often I can pass an item directly instead of a tuple with a single item. Regex functions take regular strings or regex strings, they don't force regex strings.
Being forced to use a single specific type of string in all cases is just very different from how Python has traditionally operated.
It's safer, I get that. But it's definitely less friendly, so I'll be curious to see how module maintainers decide to handle this.
Er… that’s just not correct? Python can be more liberal but it’s not always. It depends entirely on the tooling. Libraries will take time to catch up but I can definitely see people creating libraries that enforce t-strings, even if they’re deconstructing them under the hood for legacy libraries.
It works fine. It doesn't work with a float, which is for good reason. That's the whole point -- its general philosophy is to be pretty liberal with types, except when there's a good reason not to be. Heck, you can even do dumb things like:
4 + True
And get 5 back. If that's not "blindly interchanging different types for no good reason" then I don't know what is. (You can even multiply your Decimal object by False and get an answer...)
Or it's like my original example -- the Regex module isn't restricted to r-strings. It happily works with regular strings. Python's generaly philosophy is to handle input liberally. Type hinting is an add-on. It doesn't go as far as JavaScript in allowing e.g. "4"+1, but it's still awfully liberal. I just don't see how you can claim otherwise.
For the reasons discussed above, I'm not sure that it will be the case for t-strings. I think it'll take a little while for frameworks/libraries to adapt (while still maintaining backward compatibility) and a while for best practices to find their way into our linting and other tools.
I think it's way more likely that existing libraries will introduce new methods that use t-strings and are type safe, rather than entirely defeat the purpose of having a t-string API.
I'm guessing no existing functions will be extended to allow t-strings for this very reason. Instead, new functions that only accept t-strings will be created.
There's an obvious risk here, same as with strcpy (no, strncpy.. no, strlcpy... no, strcpy_s) that documentation tends to outlive code, and people keep pasting from tutorails and older code so much that the newer alternatives have a hard time cutting through the noise.
I would argue that as bad as some w3schools tutorials were, and copying from bad Stackoverflow answers, going back to MSA and the free cgi archives of the 90s, the tendency of code snippets to live on forever will only be excarbated by AI-style coding agents.
On the other hand, deprecating existing methods is what languages do to die. And for good reason. I don't think there's an easy answer here. But language is also culture, and shared beliefs about code quality can be a middle route between respecting legacy and building new. If static checking is as easy as a directive such as "use strict" and the idea that checking is good spreads, then consesus can slowly evolve while working code keeps working.
Do the python type checkers / linters / whatever have the ability to warn or error on calling certain functions? That would be nice to eventually enforce migration over to the newer functions that only take a t-string template
Yeah. A while back I was poking through some unfamiliar code and noticed that my editor was rendering a use of `datetime.utcnow()` as struck through. When I hovered it with my mouse, I got a message that that function had been deprecated.
Turns out my editor (vscode) and typechecker (pyright) saw that `datetime.utcnow()` was marked as deprecated (I know one can use the `@deprecated` decorator from Python 3.13 or `__future__` to do this; I think it was done another way in this particular case) and therefore rendered it as struck through.
And it taught me A) that `utcnow()` is deprecated and B) how to mark bits of our internal codebase as deprecated and nudge our developers to use the new, better versions if possible.
If it's not a completely new library written exclusively around templates, such code currently accepts strings and will most likely continue to accept strings for backwards compatibility.
That would be a great argument if Python wasn't a language that let you reach into the internals and define __str__() for things you shouldn't be defining it for. And that is something people will definitely do because, you know, they just need something to friggin work so they can get whatever ticket closed and keep some metric happy tracking time-to-close
I guess that is a misunderstanding on your side, about how templates work. Less hate and more love might help to avoid this type of hotheaded misconception ;-)
Why do you think changing a letter would cause a vulnerability? Which letter do you mean?
No sane library is going to do that. If they do let you pass a raw string it should be a different function with the risks clearly documented.
The thing this replaces is every library having their own bespoke API to create a prepared statement on their default/safe path. Now they can just take a template.
How about every library that wants to preserve backwards compatibility?
Or are you suggesting that e.g. every database module needs to implement a new set of query functions with new names that supports templates? Which is probably the correct thing to do, but boy is it going to be ugly...
So now you'll have to remember never to use 'execute()' but always 'execute_t()' or something.
You don't have to remember it, you can use deprecation warnings and lint tools to remind you. (Until eventually the safe API is the only API and then you really have nothing to remember.)
I’d assume their current safe function isn’t taking a string, and is taking some sort of prepared statement? So they could have it take either their prepared statement or a template, and deprecate their prepared statement.
If a library has functions taking a string and executing it as SQL they probably shouldn’t make that take a template instead, but I’d hope that’s a separate explicitly unsafe function already.
For sqlite3, it absolutely takes a regular string.
If you want to substitute parameters, you put a '?' in the string for each one, and provide an additional (optional) tuple parameter with the variables.
So no, there's no explicitly unsafe function. That's my point.
Gotcha. I’d guess they’d want to deprecate that function and create a new one that only accepts a template then, which is definitely annoying! I figured they’d already have more separation between prepared and raw strings which would make it easier.
Also I wonder how easy it will be to shoot oneself in the foot. It may be easy to accidentally make it to a string too soon and not get the proper escapeing.
That’s a library author problem, so it’s less likely since library authors tend to be fewer in number and, for popular libraries, get a reasonable number of eyes on this type of change.
Personally, this feels like a feature that is too focused on one problem to be a general feature. Python is getting huge. When people ask me if Python is easy and simple to learn I have to say "the basics, yes, but to to learn the whole language... not so much".
I feel like in this sense Go really is interesting by rejecting almost every single feature. Honestly not sure generics were worth it as they add a lot of complexity, and while they are nice, I don't need them very much. The general idea to keep the language at its original focus is the right idea IMO. C++ would be the most extreme case where the language itself barely resembles what it started out as.
Python has always been a batteries-included language, so having a go at templated string interpolation —a feature other languages have had for decades— seems like a strange gripe.
It's far more essential than little utilities like textwrap or goliath packages like Python's bundled tkinter implementation.
Also, you can also find languages like Python that have a rich ecosystem of third party templating solutions. These are often intended for things like rendering entire web pages but many of them have relatively simple ways of using their templating functionality in a fairly reasonable amount of code, if you just want to have a template format that allows interpolating values based on a template string.
So, as you can see, many other languages have this feature, as you can tell from all the examples I have shown you here.
(To spell it out for those who may find this too subtle... somehow... I'm not a fan of this simply because Python has gone from "There should be one-- and preferably only one --obvious way to do it." to "there's half-a-dozen ways to do it and if they are all wrong Python 3.x+1 will introduce a seventh" and I'm just not seeing the benefits worth the tradeoffs here.)
C# InterpolatedString is very close, with the twisty bit being that C# can rely on static typing for safety so the "f-string" and "t-string" variants use the same literal syntax and depend on what function they are passed to, whereas in both Python and Javascript they have different literal syntaxes. Python chose to use a different literal prefix to its literals ("f" versus "t") and Javascript chose to use a function-call syntax as prefix (`templateString` versus html`templateString` where html is a function in scope).
For the case like here it’s closer to FormattableString that’s what EF Core’s composable FromSql method works on top of. Both address custom interpolation but from different angles / for different scenarios.
There’s an interesting trade off around maintenance. Python’s stdlib means there’s more consistency across projects and you can assume basic things like error handling which you had to check individually on each Go program, which is the kind of stuff which adds up when you have a lot of small programs.
This is especially noticeable with AWS Lambda where you can have a lot of useful stuff running for years without doing more than bumping the runtime version every year or two, but also that is one highly opinionated architecture so it’s not globally optimal for everyone.
This is a pretty simple and useful feature. I wouldn’t say that it bloats the language too much. Descriptors and metaclasses are much more complicated and have a lot more implications and have been in the language for a veeeeery long time. Is it decades already?
This feature is not complicated, but one must keep every feature that can possibly be seen in code in their head. Even if it is familiar now, what happens when you use the feature in the one small section of code where it fits, nowhere else, and then read that code 2 years later? This is the problem with adding useful features that are only used in a few key places. I'm not saying Go is a perfect language, far from it, but limiting # of features as a general goal is something more languages should strive for IMO.
I am not arguing against that language ideally should have less features. I am arguing with “Python is getting huge”, because it’s huge and has been for many-many years :)
Yeah, Python hasn’t been a simple language for a long time, if ever. That’s probably the biggest misconception about the language - that its friendly syntax implies simple semantics. It’s not true at all.
I would say python in it's entirety is one of, if not the deepest and potentially most complex language I know. C++ is the other contender. The things you could do with metaclasses, multiple inheritance and operator overloading are quite staggering.
I'm just glad you don't have to think or even use this as a normal user of the language, most of the time or at all.
I'm truly glad that Go exists for people who like languages that are simple even to the point of frustration and I hope it never changes. But I'm glad that other languages exist for those of us for whom learning some syntax is not a barrier and having convenient ways to do common things is highly valued.
I'm a little late to the conversation (and a bit surprised to see this trending on HN) but am happy to answer any questions; I'll try to pop in throughout the day.
PEP 292's `string.Template` will remain; there are no plans to deprecate it.
PEP 750's `string.templatelib.Template` is a separate and unrelated type. Amongst many differences, unlike PEP 292, `Template` has a literal form too.
I'm hopeful that the confusion will be minimal; in practice, PEP 292 (aka $-strings) is used only in specialized cases, like flufl.i18n, a really deep I18N framework.
The PEP originally started with a similar-to-javascript syntax but over time we decided it wasn't the right way to expose these ideas in Python. There's more detail about why this approach was rejected in the PEP: https://peps.python.org/pep-0750/#arbitrary-string-literal-p...
This is exactly how Nim is. The f-string like equivalent uses a macro called "fmt" which has a short alias "&". So you can say:
import std/strformat
let world = "planet"
echo &"hello {world}"
The regular expression module does a similar thing with a `re"regular expression"` syntax or std/pegs with peg"parsing expression grammar" and so on. There are probably numerous other examples.
In general, with user-defined operators and templates and macros, Nim has all kinds of Lisp-like facilities to extend the language, but with a more static focus which helps for both correctness and performance.
This was the original proposed idea in the PEP (750), but it changed overtime. There is a section in the PEP to explain why it changed to t-strings if you are interested.
FWIW the JS equivalent is a template but tagged with a language. It has all the benefits of this template, but IDEs can easily syntax highlight the string. That seems like it would be a bit trickier to do with the Python one which is a shame.
I see each of these as distinct but overlapping; I'm (slowly) writing a guide to string formatting with all of these in mind, trying to emphasize when I'd choose one over the other. (fwiw I personally avoid % and + these days; $ is pretty uncommon in practice; f-, t-, and .format() all seem to have good unique uses.)
The last three generally shouldn't be used (`+` is sometimes fine, but not really for formatting), but I doubt we would ever get a py4 that removes them, given the stomachaches that py3 caused. It does feel odd that a t-string is just an f-string without args applied.
by making it a generic `t` you lose explicit syntax highlighting. Where something like JS template`string` could determine which syntax to use based on the template value.
I supposed when assigning it to a, variable: SyntaxRecognizableTemplate, you could give it the hint necessary.
was this discussed in the PEP?
*edit: reading the PEP-750[1] it doesn't seem like it..
But yes, the PEP leaves open an important question: how will tools decide to work with common types of content in t-strings, like HTML or SQL?
There are simple approaches that can be taken in the short term (content sniffing) and more robust approaches (type annotations, perhaps) that will take time and the broader tooling community to develop.
It was discussed in the first revision and discussion of the PEP. The decision was made to move that to follow-on work, as we discovered more about what tooling needs.
As an example, I was excited about using `Annotated` on the function to indicate the language it expected. Turns out, a lot of linters know nothing about the type system.
Why does this need to be a language feature. This could just be a separate library, we could use brackets instead of a letter before a string. I fear, Python is going down the path of C++
It being a language feature gives you controlled access to the lexical scope, such that the template string can refer to variables by name rather than having to pass each value as a parameter. Doing it via parameters is repetitive and/or error-prone.
This feature actually can't be a library. It needs to be able to preserve the string before the variables are passed in, which a library would be unable to do because f-strings immediately replace all the values.
The whole premise of t-strings is to know which values where "hard coded" and which ones are variables. A library can't possibly know that. And a function call wouldn't have access to the local variables.
The only way to do this without language support is to pass `locals()` into every function call.
Now you have me wondering how difficult it would be to have a class that takes a string and parses through globals to find the context it was called from. maybe causing an exception and abusing a traceback? or maybe we just find our own objectid.... gahh I have to try it now, but I'm setting a timer.
It was easier than I thought, but also took longer than I wanted to. turns out the inspect module provides what you need to pull it off.
This dummy example splits a string that it was given, then if one of those values is in the callers context it saves those in self.context, and has an output function to assemble it all together. Obviously this example is not very useful, but it shows how a library could do this as a class or function without the user having to pass in locals().
import inspect
class MyXString:
""" will split on whitespace and replace any string that is a variable name
with the result of str(variable)"""
def __init__(self, string):
self.string = string
caller_locals = inspect.currentframe().f_back.f_locals
self.context = {}
for key in set(string.split()):
if key in caller_locals:
self.context[key] = caller_locals[key]
def output(self):
output = self.string
for k,v in self.context.items():
output = output.replace(k,str(v))
return output
You don't have to go through all the globals, you just have to get the caller's namespace, which is fairly simple. See e.g. https://stackoverflow.com/a/6618825/27426
For this reason, I think it's not true that this absolutely had to be a language feature rather than a library. A template class written in pure Python could have done the same lookup in its __init__.
It's not as simple as "more features" == "closer to C++". Features are not equal to each other in terms of impact on language complexity.
t-strings don't interact with anything else in the language; they, as you yourself pointed out, could almost be an isolated library. That makes them low impact.
This is also true syntactically; they're just another type of string, denoted by "t" instead of "f". That's easy to fit into one's existing model of the language.
Moreover, even semantically, from the point of view of most language users, they are equivalent to f-strings in every way, so there's nothing to learn, really. It's only the library writers who need to learn about them.
Then we have to consider the upsides - the potential to eliminate SQL and HTML injection attacks. The value/cost is so high the feature a no-brainer.
If it's not a language feature, there's always a risk of fragmentation. Some people won't use it because it adds another dependency, that means fewer programmers will be familiar with it. Others will come up with their own, slightly incompatible implementation. See for example Perl and its various Object Orientation frameworks (Moose, Mouse, Moo, Mo, M, Mojolicious comes with its own...)
Other languages have a policy of prototyping such things out of core, and only adding it to the core language if it gains traction. Of course that works better if the language has a mechanism for extending the syntax out of core.
What I really don't get is how it's any different than applying whatever function you would apply to the template, on the f-string variables. So instead of:
Pretty much, yeah. The article highlights that people were using f-strings directly, and they wanted to provide an alternative for lightweight template/interpolation.
I feel like I'm still missing something when they're saying this about the example(s):
"Neither of these examples is possible with f-strings. By providing a mechanism to intercept and transform interpolated values, template strings enable a wide range of string processing use cases."
As far as I can see, anything you do with the template, you could do before building the f-string or inline as in my intial example.
With f-strings, you cannot write code to determine which portions of the resulting `str` were static and which were dynamic; with t-strings, you can. *
(As to your initial example: it's worth considering what will happen as you compose multiple bits of HTML via nesting to generate a large final page. The developer experience may become... unideal.)
You wouldn’t really do your example, though. If you’re using an f-string, you’d just directly interpolate, because it’s convenient. You wouldn’t use an extra library to properly make it safe, otherwise you’d just use a proper template library and language.
This gives you a convenient middle ground where you don’t need to learn a template library but still get safety. I can’t think of the code right now but I could see this being useful to pass in some dynamic HTML to, say, Django without having to remember to turn off escaping for that section. It can also be convenient for writing raw SQL without having to use prepared strings.
> t-strings evaluate to a new type, `string.templatelib.Template`
> To support processing, `Template`s give developers access to the string and its interpolated values before* they are combined into a final string.*
Are there any use-cases where processing a Template involves something other than (i) process each value, then (ii) recombine the results and the string parts, in their original order, to produce a new string? In other words, is the `process_template` function ever going to be substantially different from this (based on `pig_latin` from the article)?
def process_template(template: Template) -> str:
result = []
for item in template:
if isinstance(item, str):
result.append(item)
else:
result.append(process_value(item.value))
return "".join(result)
I haven't seen any examples where the function would be different. But if there aren't any, it's strange that the design requires every Template processing function to include this boilerplate, instead of making, say, a `Template.process` method that accepts a `process_value` function.
Templates don't even have to be processed into a string. The article shows an example where the Template is processed into an HTML mini-DOM. It's maybe not obvious because the DOM object is immediately stringified to show sample output, but you could imagine manipulating the DOM object in a few more steps before stringifying it, or maybe you are running in WASM in a browser and using that mini-DOM directly as a Virtual DOM passed to JS to work with.
Also, in addition to the other SQL example using "?" to fill in the "holes" for parameters in an SQL friendly way, some DBs also support named parameters, so the "hole" in the string form might be naively replaced with something like `f"@{item.expression}"` and that also forms the key in a dict to pass as parameters. (You'd want to make sure that the expression inside the template is useful as a parameter name, and not something more exotic like {1 + 3} or {thing for thing in some_list}, in which cases you are probably auto-assigning some other parameter name.)
Also, my comment was about the amount of boilerplate required, but that can be vastly reduced by writing `process_template` in a more functional style instead of the highly-imperative (Golang-like?) style used in the article. The first `process_template` example is just:
I wish they added the same thing JS has, where this "string literal prefix thingy" can be user-defined.
html`<p>${value}</p>` will actually run the function html(template). This means you can use this to "mark" a function in a way that can be detected by static analysis. Many editors will, for example, syntax highlight and lint any HTML marked this way, same with SQL, GraphQL and probably some others too.
The PEP was initially proposed this way. But due to various reasons, making it an open namespace was considered to overcomplicate the language (read: understanding coffee when reading it). Alternatively, there doesn't really seem to be much loss of ability with t-strings. Libraries can require a template as it's accepted type, instead of having to invent their own custom type and named template.
For the record the JS thing desugars to the exact same as the Python thing, so it is no more or less safe to do the syntax highlighting in Python as it is in JS.
It desugars similarly, but the Python version doesn't have a name. Any t-string is a t-string, there's no HTML t-string or SQL t-string or anything like that. It's just a t-string you can pass to a function:
html_string = t"<something />"
sql_string = t"SELECT * FROM something"
In JS, the string has a prefix that can differ between languages, e.g.:
Except your labels are incorrect because neither `html_string` nor `sql_string` are strings, they're both Template objects, and the sink function is the one which processes it. No processing has happened to them by the end of the snippet, beyond creating the template object itself.
Sure, choose different variable names, who cares. The essential difference is that the language is referenced at the declaration site, not the usage site, which makes the syntax highlighting far easier.
Please engage with my point instead of criticizing trivialities.
> Please engage with my point instead of criticizing trivialities.
Your complete misunderstanding of what's happening is not a triviality.
> The essential difference is that the language is referenced at the declaration site, not the usage site, which makes the syntax highlighting far easier.
Javascript has no built-in template tags beyond `String.raw`. If tooling has the capabilities to infer embedded language from arbitrary third party libraries, I would hope they have the ability to do utterly trivial flow analysis and realise that
html(t"<something />")
means the template string is pretty likely to be HTML content.
Yes. It's a weak heuristic, but it's EXACTLY the same weak heuristic that JS is applying!
IN other words, since custom template tags in JS *are literally just function calls* when a JS environment syntax highlights the code as HTML it's doing so based on an extremely weak heuristic (the identifier for the interpolation function is named "html"). Both Python and JS have the same problem.
I think his point would be clearer if we focused on typing the usages statically. Consider `html(this_is_a_sql_template)` vs. `html"SELECT * FROM ..."` or `thing_that_consumes_html_template_type(oops_a_sql_template_type)`.
Come on, you're just being rude for no good reason. A badly chosen variable name doesn't show a "complete misunderstanding". Yes, the variable should have been named `html_template` instead of `html_string` - how often do I have to acknowledge this before you accept it?
And it's obviously more complex to do syntax highlighting when the declaration site and usage site are possibly split apart by variable assignments etc. Yes, in the case you showed syntax highlighting is easy, but what if the `html` function takes more parameters, doesn't take the template as the first parameter, etc? There's a lot of possible complexity that tagged template literals don't have. Thus they are easier to do highlighting for. This is objectively true.
Tagged template literals in JS have all that complexity. All of it. That tools you trust lie and pretend that's not the case doesn't make the language spec say anything different
No, they literally don't, because they don't support these features!
You can't split apart the declaration of the template literal and the "tagging". The tag is always part of the declaration, which it doesn't have to be in Python, as I've showed.
You can't pass additional parameters to the tag function, it's always just the template & values. In Python, you can pass as many parameters as you want to the usage site, e.g.
It just sounds like you don't know JS very well, because in JS you can definitely split apart the declaration and the tag with ease. The thing implementing the tag is just a function after all: https://jsfiddle.net/rd2f1kot/
you already have a string in the `template` variable. There's no access to the individual values anymore. It's already done. It's a string. No template. You can't pull apart the literal declaration and the tagging.
Are we now done with this ridiculous game of deliberate misunderstandings?
Sorry for some reason I can't reply to the deeper posts. Depth limit I guess. You asked which editors could support syntax highlighting once the tag and the content that needs to be syntax highlighted are split apart. Currently there are none, though I am writing one that will be able to.
Python should be able to detect the magic syntactic pattern just the same way JS does and use that for syntax higlighting. In JS the magic syntactic pattern for triggering HTML syntax highlighting is:
html`<doc/>`
In Python the magic syntactic pattern would be:
html(t"<doc />")
My point in showing that JS counterexample was to demonstrate that the real reason people don't do that kind of thing isn't that they can't, it's that they like having syntax highlighting. That means the approach should work just as well in Python. This is the case even though the heuristic involved is very weak. Changing the name of the identifier or breaking into multiple expressions would be enough to break the heuristic in either language, which is why I think it's a really weak heuristic and dangerous pitfall for developers who might mistake the coloring for information about how the runtime sees that data (which is normally what syntax highlighting is for)
So now we have moved from "tagged template literals have all the complexity of Python templates" to "if you define a specific template tag and use that, you can replicate one feature of Python templates". No mention of the other example I mentioned (which, by the way, wasn't an exhaustive list).
Now, I'll just ignore that you're still deliberately misrepresenting me in the hopes of gaining some actual knowledge from this discussion - please show me: which editor supports syntax highlighting for the specific example you just mentioned? After all, that was the topic of discussion - not whether it's possible to delay "tagging", but whether it's easier to do syntax highlighting for JS template tags. Please show me an existing editor, IDE or git repo for a tool that would highlight your specific example based on the `html(...template)` call in line 4 (so no heuristics based on line 3). Surely you're not just throwing random examples at the wall to see what sticks, right? You've actually been following the discussion and are arguing in the context of it?
No, it doesn't, it references the language at the declaration site, because the declaration site always is the usage site. You can't split them apart. You can split them apart in Python - see the example in my first comment.
The JS version actually desugars to something much more primitive, and less convenient: in JS a template tag receives one parameter which is an array of n+1 strings, and then n parameters for the interpolated values, and has to iterate alternatively on both sequences.
You can do that in python by accessing the `strings` and `values`, but I expect most cases will simply iterate the template, yielding a unified typed view of literal strings and interpolated values.
How do these interact with i18n? Can I load a translated t-string with `_(t"")` from a .po file? Can it include variable names and arbitrary code inside lambdas?
Debate around the usefulness aside, are there any linter rules for warning about f-strings in light of this? I can easily see where mistaking one for the other would cause problems. For context, I'm thinking specifically about tools like Black and MyPy.
The runtime and static type of the template string is different to fstring (Template vs str). Unless you’re passing them somewhere that accepts strings, you can’t go wrong.
I actually quite like the simplicity of this design over tagged literals in JS.
TL;DR: like f-strings, all {foo} expressions in the t-string are evaluated immediately, but instead of immediately concatenating everything into a single result string, the t-string evaluation returns a Template object that keeps the interpolation results and the surrounding strings separate. This lets subsequent logic decide whether the interpolation results need any special escaping before concatenating them with the strings around them.
In other words, t-strings are basically f-strings where the final concatenation is delayed. And indeed, you can trivially implement f-strings using t-strings by performing a simple, non-escaped concatenation step: https://peps.python.org/pep-0750/#example-implementing-f-str...
> This lets subsequent logic decide whether the interpolation results need any special escaping before concatenating them with the strings around them
This sounds like unnecessary fluff in what was supposed to be a simple language. I'm worried Python is turning into C++42 with 65535 ways to do one simple thing.
Why not just:
f'SELECT * FROM `{esc(table)}` WHERE name = "{esc(name)}"'
It's easy to forget the `esc` function. How does the recipient check (or type check) that it was called in all the right places?
Most DBs support parameterized queries which can be cached for performance. How do you pick out the parameters from that and replace those parts of the strings with the DB's parameter placeholders?
t'Select * from {table} where name = {name}'
Looks very similar, but execution engine has access to all the individual parts, making it very easy to add placeholders such as:
('Select * from ? where name = ?`, table, name)
Or even (if the DB supports it), has access to the expressions inside the string and can use named parameters:
('Select * from @table where name = @name', { "table": table, "name": name })
That's really nice for debugging, depending on your DB engine.
In every DB engine that supports it, parameterized SQL is even safer than escape syntaxes because parameters are passed in entirely different parts of the binary protocols and don't need to rely on just string manipulation to add escape sequences.
While your code is a valid alternative way to implement @haberman's description, the feature is actually much more flexible.
The "subsequent logic" has full access to the interpolation results and strings. Not only can it escape the results, it can do whatever it wants to them. It can also do whatever it wants to the strings, and then combine everything in any way it likes - it's not even necessary that the final result is a string.
The other PEP example shows generating HTML attributes from a passed-in dictionary. HTML has a number of places where this is helpful, if you have original data.
No, I mean that if Django's template engine internally switched over its implementation to enable templating (as a functionality) to use these new t-strings. If t-strings are more highly optimized within Python, it could mean a performance boost.
I don't think things would be very different if Guido were still BDFL. He's second-author of the t-strings PEP, and has been an author of most other major PEPs in recent releases (including the walrus operator, PEG parser, and pattern matching).
I really was on the side of being generally willing to accept new python features, but this is getting ridiculous. What an utterly pointless thing to bloat the language with. At this point my moving to clojure as my first line language of choice is only accelerating.
This is of the category "things I wouldn't want to use even for the specific hyper niche things they're intended for". What even does a "t-string" represent? Because it's clearly not a string of any kind, it's a weird kind of function call notation. The programmer sees something that looks like string formatting, but the program executes some arbitrary procedure that might not return a string whatsoever.
For me, this is the best feature to land in python for 6 years. JS has had this and it allows my code to be completely safe from SQL injection, which is an absolutely incredible feature, given SQL injection has been the #1 vulnerability for a long time.
Thanks Nick for this response and all the time you've spent explaining. It's funny, I looked back at the comments on f-strings before they landed. They also got similar complaints about bloat. And yet, my uneducated guess: very popular.
I'm not the OP but I'm guessing with OP moving to Clojure that the bloat is basically any special syntax or special language feature that basically boils down to a function call or a let statement. A lot of functional programming languages have minimalistic expression syntax and they are just as expressive as OP needs them to be.
Not sure about introducing yet another string prefix. Between f-strings, raw strings, and i18n stuff, it’s already getting crowded. Curious how readable this will be in large codebases.
How would this be different from a function sql() that operates on one of these new t-strings?
The syntactic sugar of changing it from sql(t"...") doesn't seem particularly valuable. The novel thing about t-strings is that they change the parsing at compile-time.
It’s different from a function the same way f”” is different from f(“”) and t”” is different from t(“”)
There’s nothing stopping you from building a Python function that parses a string looking for {} and then searching globals for those variables. And you can extend that to also do some code execution and formatting.
To me the real sugar of f-strings is that the editor knows that it’s a template and not just a string. Expanding this to having SQL and regex syntax highlighting, linting and code formatting inside my Python code is a pretty cool prospect.
Additionally, it will probably be confusing that it is called a t-string but it is actually a constructor for a Template object and not string at all. I would rather see a new special term `template` than this.
No. F-strings should still be the default. T-strings aren't usable directly, and don't have a `str` like API, so they aren't even compatible, intentionally.
Seems pretty neat so far, but I don't understand the motivation behind not allowing you to call str(template) and get the template as a normal string. I could imagine it being very useful to be able to gather up the template itself in a string to do stringy things with.
The only reason I could imagine, is if you are trying to protect developers from themselves, which kinda goes against the "we're all adults here" mentality that makes Python so great. I suppose it's easy enough to add that functionality, but come on.
> If you’ve worked with JavaScript, t-strings may feel familiar. They are the pythonic parallel to JavaScript’s tagged templates.
The syntax is template literals, not just "tagged templates". Which is a huge difference: template literals still act as real strings. They don't need a tag prefix to work, you have the option to tag them if and when needed.
As far as I understand it, t-strings can't do that. They're not strings, and you can't even coerce them into strings, you have to run them through a processor before they become a string. So they're nothing like JS's template literals, they're syntactic sugar for forming "an instance of an object that needs to be passed into a function that returns a string".
So I don't look forward to folks preferring f-strings over t-strings even when they really shouldn't, simply because "having to constantly convert them from not-a-string to a string is a hassle". If only they'd worked like JS template literals.. that would have been fantastic.
Honestly think this is a more useful feature and elegant solution than the walrus operator that was added. Formatting query strings has always felt messy especially with different DBs having their own non-standard ways of doing it.
It’s injection safe and compostable, and the resulting object retains the original values you interpolate in. This makes it useful for building SQL queries with prepared arguments for example.
It’s on a meta level: instead of formatting the string, it returns an object that contains both the format string and its argument. Library author can then implement whatever format function they want, for example one that escapes the interpolated strings.
f"foo is {foo} and {bar=}"
"foo is {} and bar={}".format(foo, bar)
are equivalent.
t-strings are actually not strings, but Template objects, giving access to both the templating string and the parameters for processing. Sibling comments describe it as a custom .format implementation in that sense - it's f-string-like sugar where you're also allowed to take control of the .format function that it's sugar for.
Sure, this avoids issues with SQL injections. However, I have a hard time imagining any developer who would both make such fundamental errors with f-strings currently and also switching to this option when it ships.
Seems like a self selection which renders this meaningless, to some extent :/
> However, I have a hard time imagining any developer who would both make such fundamental errors with f-strings currently and also switching to this option when it ships.
t-strings are a different type (both static and dynamic), f-strings are not. So t-strings can be mandated at the API level, forcing the developer into "proper" usage.
That is, you need third-party tools to differentiate between
some_call("safe literal string")
and
some_call(f"unsafe dynamically created string")
That is not the case when it comes to t-strings, `some_call` can typecheck internally that it got a t-string, and reject regular strings entirely.
Although some space probably needs to be made for composing t-strings together in case of e.g. runtime variation in items or their count. Facetting for instance. I don't know if that's a native affordance of t-strings.
sqlalchemy doesn’t really accepts strings - if you do, you need to pass them into a “conn.execute(text(…))”, so end users should not face a breaking change.
If this is just for sql queries ... it'd be overkill especially where you need to compare the usual PREPARE statements with the hassle of keeping everyone on 3.14 and above.
I enjoy f-strings, I guess some people need these.
And I love Python but, having been through 2->3 ( occasionally still going through it! ) whenever I see a new language feature my first thought is "Thank goodness it doesn't break everything that went before it".
Yeah but it's been 17 years, maybe it's time to put the PTSD behind us. We're almost at a point where the current generation of programmers wasn't even programming when that happened.
> We're almost at a point where the current generation of programmers wasn't even programming when that happened
I've been programming with Python since 2006, I think most of the systems were based on 2.4 at the time. I've been one of those who switched to Python 3 somewhat late, waiting for some major libraries to ship python 3 packages - celery and Twisted were one of the biggest holdouts - so I remember that the first project where all my dependencies were ready for python 3 was around 2015.
This is to say: even seasoned developers who were conservative around the migration have spent more time working with Python 3 than Python 2. There simply is no reason anymore to be talking about python 2.
The last time I touched a large Py2 project was in 2018 when I ported it to Py3. So, I have 18 years of Py2, probably 6 years of overlap, and 7 years of pure Py3. That means I still have a lot more Py2 than Py3 time.
Buuuttt, I'm so over the transition. It’s ancient now and I agree that we can stop fretting about it.
Python2 code didn't disappear when Python3 came out. At my work we're _still_ occasionally having to help people migrate code that was written for python2
I feel like this can be solved another way. S=f”my good code #### {potentially_evil_user_input} #### my good code again” then work around the ####. Of course, even better, S=evil_user_input and do a scrub on S first.
This is such a strange take on t-strings. The only way for anything to infer that the template string is supposed to turn into valid HTML or SQL is to base it of the apparent syntax in the string, which can only be done in an ad-hoc fashion and has nothing to do with the template string feature.
The way the feature has been designed there is no indication in the string itself what type of content it is or what it will eventually be converted to. It’s all handled by the converting function.
As others have added, something like sql”select * from {table}” would have been able to do this, but there’s not even any guarantees that something that is in a template that will be converted into valid sql by a converting function should be any type of valid sql prior to that conversion. For all you know t“give me {table} but only {columns}” might be a converted into valid sql after the template is processed.
I understand why this seems strange at first!
As Paul mentioned, we spent quite a lot of time considering these issues as PEP 750 came together. In the end, we concluded (a) the PEP leaves open quite a few potential approaches for tools to adopt (not just the one you suggest, as others here have pointed out), and (b) it's ultimately something that the broader tooling community needs to rally around and should probably be out of scope for the PEP itself.
But without having that background, it might indeed seem strange that I am hopeful we'll see the ecosystem adapt! :-)
JavaScript's tagged template literals are actually about as flexible as this, since you can dynamically choose the tag function, it's just very rare to do so, so tools assume a lot based on the name of the function. Python tools can basically do the same thing, and just not support t-strings that aren't nested inside a well-named processing function.
Not the only thing. You can also look at how it is used. Your editor could know of how some popular libraries use t-strings, track which t-strings get passed into functions from those libraries, and use that to assume what grammar the t-string should follow.
Is that cheating? In some sense, yes, but it also is useful and likely will be worth it for quite a few programmers.
We hope to get a community around all of this, stuff at PyCon US, EuroPython, etc. and work some of this out. The JSX/TSX world really has good tooling. We can provide that for those that want it, perhaps better on some aspects.
Writing `query: SQL = t"SELECT ..."` is a small price to pay for such a DX boost.
1. Allowing library developers to do whatever they want with {} expansions is a good thing, and will probably spawn some good uses.
2. Generalizing template syntax across a language, so that all libraries solve this problem in the same way, is probably a good thing.
https://github.com/darioteixeira/pgocaml
Note that the variables are safely and correctly interpolated at compile time. And it's type checked across the boundary too, by checking (at compile time) the column types with the live database.
But my two cents is that we're pretty lucky it's python that has taken off like a rocket. It's not my favorite language, but there are far worse that it could have been.
Also:
Is dangerously close to: A single character difference and now you've just made yourself trivially injectible.I don't think this new format specifier is in any way applicable to SQL queries.
> Caching parameterized prepared statements, etc.
Templates give you all the data you need to also build things like cacheable parameterized prepared statements. For DB engines that support named parameters you can even get the interpolation expression to auto-name parameters (get the string "name" from your example as the name of the variable filling the slot) for additional debugging/sometimes caching benefits.
All of which can be implemented on top of template strings.
> A single character difference and now you've just made yourself trivially injectible.
It's not just a one character difference, it's a different type. So `db.execute` can reject strings both statically and dynamically.
> I don't think
Definitely true.
> this new format specifier is in any way applicable to SQL queries.
It's literally one of PEP 750's motivations.
> Definitely true.
The rest of your comment is valuable, but this is just mean-spirited and unnecessary.
> It's not just a one character difference, it's a different type. So `db.execute` can reject strings both statically and dynamically.
in this case, that's not actually helpful because SQL statements don't need to have parameters, so db.execute will always need to accept a string.
No. A t-string with no placeholders is perfectly fine. You can use that even if you have no parameters.
I thought we left middle-school playground tactics behind.
That would be in addition to doing any runtime checks.
I’d consider that an invalid use case:
1. You can create a template string without placeholders.
2. Even if the caller does need to pass in a string (because they’re executing from a file, or t-strings don’t support e.g. facetting) then they can just… wrap the string in a template explicitly.
Python is notorious for misguided motivations. We're not "appealing to authority" here. We're free to point out when things are goofy.
In Javascript, sql`where id = ${id}` is dangerously close to normal string interpolation `where id = ${id}`, and db libs that offer a sql tag have query(stmt) fns that reject strings.
Agree. And the mere presence of such a feature will trigger endless foot-gunning across the Python database ecosystem.
I had to look SEVERAL times at your comment before I noticed one is an F and the other is a T.
This won’t end well. Although I like it conceptually, this few pixel difference in a letter is going to cause major problems down the road.
CS has survived for decades with 1 and 1.0 being completely different types.
https://docs.python.org/3/library/sqlite3.html
https://www.psycopg.org/docs/cursor.html
https://dev.mysql.com/doc/connector-python/en/connector-pyth...
I'd have to take a look at the order things happen in shell, but you might even be able to increase security/foot-gun-potential a little bit here by turning this into something like `stat "$( base64 -d [base64 encoded content of some_file] )"`.
In order for a library to accept t-strings, they need to make a new function. Or else change the behavior and method signature of an old function, which I guess they could do but any sanely designed library doesn’t do.
Handling t-strings will require new functions to be added to libraries.
To clarify even more:
The problem is not writing by mistake t instead of f => this is what we want and then for this we implement a new function
The problem is writing f instead of t => and this will silently work I assume (not a Python dev just trying to understand the language design)
In the fullness of time it has no reason to. Even in the worst case scenario where you have to compose the query dynamically in a way t-strings can’t support, you can just instantiate a Template object explicitely.
I get the general case, but even then it seems like an implicit anti-pattern over doing db.execute(f"QUERY WHERE name = {safe(name)}")
And further, if `safe` just returns a string, you still lose out on the ability for `db.execute` to pass the parameter a different way -- you've lost the information that a variable is being interpolated into the string.
I'd prefer the second, myself.
And you add the safety inside db.safe explicitly instead of implicitly in db.execute.
If you want to be fancy you can also assign name to db.foos inside db.safe to use it later (even in execute).
I think one thing you might be missing is that in the t-string version, `db.execute` is not taking a string; a t-string resolves to an object of a particular type. So it is doing your `db.safe` operation, but automatically.
At least db.safe says what it does, unlike t".
`db.execute(Template)` and `db.unsafeExecute(str)`
also, you're trusting that the library implementer raises a runtime exception if a string a passed where a template is expected. it's not enough to rely on type-checks/linting. and there is probably going to be a temptation to accept `db.execute(sql: Union[str, Template])` because this is non-breaking, and sql without params doesn't need to be templated - so it's breaking some stuff that doesn't need to be broken.
i'm not saying templates aren't a good step forward, just that they're also susceptible to the same problems we have now if not used correctly.
Template is also more powerful/concise in that the stringify function can handle the "formatting" args however it looks.
Note also, that there's no requirement that the template ever become a str to be used.
Yes, you could require consumers to explicitly sanitize each parameter before it goes into the f-string, or, because it has the structure of what is fixed and what is parameters, it can do all of that for all parameters when it gets a t-string.
The latter is far more reliable, and you can't do it with an f-string because an f-string after creation is just a static string with no information about construction.
For me it just makes it easier to identify as safe, because it might not be obvious at a glance that an interpolated template string is properly sanitised.
Yes, the idea is that by having this in the language, library authors will write these implementations for use cases where they are appropriate.
Using a t-string in a db-execute which is, should be as safe as using external parameters. And using a non-t-string in that context should (eventually) be rejected.
The key point here is that a "t-string" isn't a string at all, it's a new kind of literal that's reusing string syntax to create Template objects. That's what makes this new feature fundamentally different from f-strings. Since it's a new type of object, libraries that accept strings will either have to handle it explicitly or raise a TypeError at runtime.
You might have implemented the t-string to save the value or log it better or something and not even have thought to check or escape anything and definitely not everything (just how people forget to do that elsewhere).
You're right that the authors of such libraries could choose to do something different with the template parameter. But none of them will, for normal interface design reasons.
A library author could also write an implementation of a `plus` function on a numerical type that takes another numerical type, and return a string with the two numbers concatenated, rather than adding them together.
But nobody will do that, because libraries with extremely surprising behavior like that won't get used by anybody, and library authors don't want to write useless libraries. This is the same.
Just because templates (or the previous syntax of passing in variables separately) could be used in a way that's equivalent (safety-wise) to an f-string by a poorly designed library does not mean that they add nothing over an f-string in general - they move the interpolation into db.execute where it can do its own sanitization and, realistically, sqlite3 and other libraries explicitly updated to take these will do proper sanitization.
imagine writing a SqL where u put user input into query string directly.
now remember its 2025, lie down try not to cry.
This way you could encode such identifier directly in the t-string variable rather than with some "out-of-band" logic.
It does, the `Interpolation` object contains an arbitrary `format_spec` string: https://peps.python.org/pep-0750/#the-interpolation-type
However I think using the format spec that way would be dubious and risky, because it makes the sink responsible for whitelisting values, and that means any processing between the source and sink becomes a major risk. It's the same issue as HTML templates providing `raw` output, now you have to know to audit any modification to the upstream values which end there, which is a lot harder to do than when "raw markup" values are reified.
> rather than with some "out-of-band" logic.
It's the opposite, moving it to the format spec is out of band because it's not attached to values, it just says "whatever value is here is safe", which is generally not true.
Unless you use the format spec as a way to signal that a term should use identifier escaping rules rather than value escaping rules (something only the sink knows), and an `Identifier` wrapper remains a way to bypass that.
This should be quiet common in the SQL applications. It will be nice to write t"select {name:id} from {table:id} where age={age}" and be confident that the SQL will be formatted correctly, with interpolations defaulting to (safe) literal values.
I completely disagree with this. Look what happened to Log4J when it was given similar freedoms.
A library can extend an existing database library like 'pg' so that PgClient#query() and PgPool#query() require string template statements.
That way 'pg' can continue working with strings, and people who want nice templated strings can use the small extension library, and the small extension library makes it impossible to accidentally pass strings into the query functions.
Having to write
even when there's nothing to format in is not a big imposition.Paging asottile - any plans to make a `future-tstrings`? :)
`future-fstrings` (https://pypi.org/project/future-fstrings/) was a real QOL improvement for our team for a year or 2 around 2019 before we got onto Python 3.x.
In fact, the repo of a companion project from the author has the ticket that spawned the work leading to t-strings: https://github.com/jviide/htm.py/issues/11
This would be the nicest way to use SQL I have seen yet.
Having more control over the interpolation of string values is a win IMO.
Prepared statements were the recommended way to run SQL queries when I was starting with PHP 15 years ago, anyone writing code vulnerable to SQL injection at this point should not be writing code.
EF/EF Core has existed for years :)
https://learn.microsoft.com/en-us/ef/core/querying/sql-queri...
Generally annoying experience if you have to clock in and out every day to watch that UI break your database relations whenever you click save.
This was a completely separate, legacy extension of VS, not EF let alone EF Core.
That's where the problem is though -- in most cases it probably won't blow up.
Plenty of SQL queries don't have any parameters at all. You're just getting the number of rows in a table or something. A raw string is perfectly fine.
Will sqlite3 really disallow strings? Will it force you to use templates, even when the template doesn't contain any parameters?
You can argue it should, but that's not being very friendly with inputs, and will break backwards compatibility. Maybe if there's a flag you can set in the module to enable that strict behavior though, with the idea that in a decade it will become the default?
There's definitely a backwards compatibility hurdle of switching to a template-only API, but a template-only API doesn't look that much "less friendly" with inputs, when the only difference is a `t` before every string, regardless of number of parameters.
I never put an f in front of a string if I'm not putting variables within it.
And I'm generally used to Python inputs being liberal. I can usually pass a list if it expects a tuple; I can pass an int if it expects a float; often I can pass an item directly instead of a tuple with a single item. Regex functions take regular strings or regex strings, they don't force regex strings.
Being forced to use a single specific type of string in all cases is just very different from how Python has traditionally operated.
It's safer, I get that. But it's definitely less friendly, so I'll be curious to see how module maintainers decide to handle this.
Are you claiming it's traditionally common in Python to be strict with inputs, and that being liberal is the exception?
Yes, it’s common for Python to be strict for inputs when the types are different. For example, try:
Decimal(‘3.0’) / 1.5
You’ll get an error and for good reason.
Or it's like my original example -- the Regex module isn't restricted to r-strings. It happily works with regular strings. Python's generaly philosophy is to handle input liberally. Type hinting is an add-on. It doesn't go as far as JavaScript in allowing e.g. "4"+1, but it's still awfully liberal. I just don't see how you can claim otherwise.
I would argue that as bad as some w3schools tutorials were, and copying from bad Stackoverflow answers, going back to MSA and the free cgi archives of the 90s, the tendency of code snippets to live on forever will only be excarbated by AI-style coding agents.
On the other hand, deprecating existing methods is what languages do to die. And for good reason. I don't think there's an easy answer here. But language is also culture, and shared beliefs about code quality can be a middle route between respecting legacy and building new. If static checking is as easy as a directive such as "use strict" and the idea that checking is good spreads, then consesus can slowly evolve while working code keeps working.
Turns out my editor (vscode) and typechecker (pyright) saw that `datetime.utcnow()` was marked as deprecated (I know one can use the `@deprecated` decorator from Python 3.13 or `__future__` to do this; I think it was done another way in this particular case) and therefore rendered it as struck through.
And it taught me A) that `utcnow()` is deprecated and B) how to mark bits of our internal codebase as deprecated and nudge our developers to use the new, better versions if possible.
Now whether maintainers introduce `getSafe` and keep the old behavior intact, or make a breaking change to turn `get` into `getUnsafe`, we will see
Why do you think changing a letter would cause a vulnerability? Which letter do you mean?
The thing this replaces is every library having their own bespoke API to create a prepared statement on their default/safe path. Now they can just take a template.
Or are you suggesting that e.g. every database module needs to implement a new set of query functions with new names that supports templates? Which is probably the correct thing to do, but boy is it going to be ugly...
So now you'll have to remember never to use 'execute()' but always 'execute_t()' or something.
If a library has functions taking a string and executing it as SQL they probably shouldn’t make that take a template instead, but I’d hope that’s a separate explicitly unsafe function already.
If you want to substitute parameters, you put a '?' in the string for each one, and provide an additional (optional) tuple parameter with the variables.
So no, there's no explicitly unsafe function. That's my point.
I feel like in this sense Go really is interesting by rejecting almost every single feature. Honestly not sure generics were worth it as they add a lot of complexity, and while they are nice, I don't need them very much. The general idea to keep the language at its original focus is the right idea IMO. C++ would be the most extreme case where the language itself barely resembles what it started out as.
It's far more essential than little utilities like textwrap or goliath packages like Python's bundled tkinter implementation.
For instance, Python has the % operator that is a template format that allows interpolating values based on a template string with a variety of printf-like features: https://python-reference.readthedocs.io/en/latest/docs/str/f...
Also, Python has the .format method on strings, which is a template format that allows interpolating values based on a template string: https://www.geeksforgeeks.org/python-string-format-method/
As another example, Python has f-strings that are a template format that allows interpolating values based on a template string: https://www.geeksforgeeks.org/formatted-string-literals-f-st...
Also, you can also find languages like Python that have a rich ecosystem of third party templating solutions. These are often intended for things like rendering entire web pages but many of them have relatively simple ways of using their templating functionality in a fairly reasonable amount of code, if you just want to have a template format that allows interpolating values based on a template string.
So, as you can see, many other languages have this feature, as you can tell from all the examples I have shown you here.
(To spell it out for those who may find this too subtle... somehow... I'm not a fan of this simply because Python has gone from "There should be one-- and preferably only one --obvious way to do it." to "there's half-a-dozen ways to do it and if they are all wrong Python 3.x+1 will introduce a seventh" and I'm just not seeing the benefits worth the tradeoffs here.)
Java 22 had the feature as preview but it was removed in 23, it'll come back after some refinement.
This is especially noticeable with AWS Lambda where you can have a lot of useful stuff running for years without doing more than bumping the runtime version every year or two, but also that is one highly opinionated architecture so it’s not globally optimal for everyone.
I'm just glad you don't have to think or even use this as a normal user of the language, most of the time or at all.
I just want this so badly, it's the main reason I drift back to JS:
;-)
I'm a little late to the conversation (and a bit surprised to see this trending on HN) but am happy to answer any questions; I'll try to pop in throughout the day.
[1] https://peps.python.org/pep-0292/
PEP 750's `string.templatelib.Template` is a separate and unrelated type. Amongst many differences, unlike PEP 292, `Template` has a literal form too.
I'm hopeful that the confusion will be minimal; in practice, PEP 292 (aka $-strings) is used only in specialized cases, like flufl.i18n, a really deep I18N framework.
I am wondering what is the reason behind not using a similar syntax to JavaScript? Seems simpler to me.
name="A$ron"
z("echo Hello {name}")
Note that this is not an f-string. The z function expands the variables by parsing this string and accessing its caller's local variables.
https://github.com/NightMachinery/brish
In general, with user-defined operators and templates and macros, Nim has all kinds of Lisp-like facilities to extend the language, but with a more static focus which helps for both correctness and performance.
If you pass a "t-string" to a framework, it can force escaping.
What you suggest is to rely on escaping by the user (dev), who, if he was aware, would already escape.
Unless you'd suggest that it would still return a template, but tagged with a language.
I like F strings a lot, but for the most part I think all of the various X-strings should just be classes that take a string as an argument.
- t-strings
- f-strings
- %-operator
- +-operator
- str.format()
I see each of these as distinct but overlapping; I'm (slowly) writing a guide to string formatting with all of these in mind, trying to emphasize when I'd choose one over the other. (fwiw I personally avoid % and + these days; $ is pretty uncommon in practice; f-, t-, and .format() all seem to have good unique uses.)
I supposed when assigning it to a, variable: SyntaxRecognizableTemplate, you could give it the hint necessary.
was this discussed in the PEP?
*edit: reading the PEP-750[1] it doesn't seem like it..
[1] https://peps.python.org/pep-0750/#the-interpolation-type
But yes, the PEP leaves open an important question: how will tools decide to work with common types of content in t-strings, like HTML or SQL?
There are simple approaches that can be taken in the short term (content sniffing) and more robust approaches (type annotations, perhaps) that will take time and the broader tooling community to develop.
As an example, I was excited about using `Annotated` on the function to indicate the language it expected. Turns out, a lot of linters know nothing about the type system.
This dummy example splits a string that it was given, then if one of those values is in the callers context it saves those in self.context, and has an output function to assemble it all together. Obviously this example is not very useful, but it shows how a library could do this as a class or function without the user having to pass in locals().
For this reason, I think it's not true that this absolutely had to be a language feature rather than a library. A template class written in pure Python could have done the same lookup in its __init__.
https://news.ycombinator.com/item?id=43752889
t-strings don't interact with anything else in the language; they, as you yourself pointed out, could almost be an isolated library. That makes them low impact.
This is also true syntactically; they're just another type of string, denoted by "t" instead of "f". That's easy to fit into one's existing model of the language.
Moreover, even semantically, from the point of view of most language users, they are equivalent to f-strings in every way, so there's nothing to learn, really. It's only the library writers who need to learn about them.
Then we have to consider the upsides - the potential to eliminate SQL and HTML injection attacks. The value/cost is so high the feature a no-brainer.
Other languages have a policy of prototyping such things out of core, and only adding it to the core language if it gains traction. Of course that works better if the language has a mechanism for extending the syntax out of core.
Meanwhile, pytest is still not part of the standard library.
https://www.psycopg.org/psycopg3/docs/api/sql.html
(while I also agree it gets crowded with yet another string prefix)
"Neither of these examples is possible with f-strings. By providing a mechanism to intercept and transform interpolated values, template strings enable a wide range of string processing use cases."
As far as I can see, anything you do with the template, you could do before building the f-string or inline as in my intial example.
(As to your initial example: it's worth considering what will happen as you compose multiple bits of HTML via nesting to generate a large final page. The developer experience may become... unideal.)
* (barring undesirable hacks with inspect, etc.)
This gives you a convenient middle ground where you don’t need to learn a template library but still get safety. I can’t think of the code right now but I could see this being useful to pass in some dynamic HTML to, say, Django without having to remember to turn off escaping for that section. It can also be convenient for writing raw SQL without having to use prepared strings.
> To support processing, `Template`s give developers access to the string and its interpolated values before* they are combined into a final string.*
Are there any use-cases where processing a Template involves something other than (i) process each value, then (ii) recombine the results and the string parts, in their original order, to produce a new string? In other words, is the `process_template` function ever going to be substantially different from this (based on `pig_latin` from the article)?
I haven't seen any examples where the function would be different. But if there aren't any, it's strange that the design requires every Template processing function to include this boilerplate, instead of making, say, a `Template.process` method that accepts a `process_value` function.Also, in addition to the other SQL example using "?" to fill in the "holes" for parameters in an SQL friendly way, some DBs also support named parameters, so the "hole" in the string form might be naively replaced with something like `f"@{item.expression}"` and that also forms the key in a dict to pass as parameters. (You'd want to make sure that the expression inside the template is useful as a parameter name, and not something more exotic like {1 + 3} or {thing for thing in some_list}, in which cases you are probably auto-assigning some other parameter name.)
Also, my comment was about the amount of boilerplate required, but that can be vastly reduced by writing `process_template` in a more functional style instead of the highly-imperative (Golang-like?) style used in the article. The first `process_template` example is just:
And the second is something like:html`<p>${value}</p>` will actually run the function html(template). This means you can use this to "mark" a function in a way that can be detected by static analysis. Many editors will, for example, syntax highlight and lint any HTML marked this way, same with SQL, GraphQL and probably some others too.
Please engage with my point instead of criticizing trivialities.
Your complete misunderstanding of what's happening is not a triviality.
> The essential difference is that the language is referenced at the declaration site, not the usage site, which makes the syntax highlighting far easier.
Javascript has no built-in template tags beyond `String.raw`. If tooling has the capabilities to infer embedded language from arbitrary third party libraries, I would hope they have the ability to do utterly trivial flow analysis and realise that
means the template string is pretty likely to be HTML content.IN other words, since custom template tags in JS *are literally just function calls* when a JS environment syntax highlights the code as HTML it's doing so based on an extremely weak heuristic (the identifier for the interpolation function is named "html"). Both Python and JS have the same problem.
And it's obviously more complex to do syntax highlighting when the declaration site and usage site are possibly split apart by variable assignments etc. Yes, in the case you showed syntax highlighting is easy, but what if the `html` function takes more parameters, doesn't take the template as the first parameter, etc? There's a lot of possible complexity that tagged template literals don't have. Thus they are easier to do highlighting for. This is objectively true.
You can't split apart the declaration of the template literal and the "tagging". The tag is always part of the declaration, which it doesn't have to be in Python, as I've showed.
You can't pass additional parameters to the tag function, it's always just the template & values. In Python, you can pass as many parameters as you want to the usage site, e.g.
In Python you can do this:
This is simply not possible in JS, because the template literal always must have the tag attached. You can't split them apart. If you try: you already have a string in the `template` variable. There's no access to the individual values anymore. It's already done. It's a string. No template. You can't pull apart the literal declaration and the tagging.Are we now done with this ridiculous game of deliberate misunderstandings?
Python should be able to detect the magic syntactic pattern just the same way JS does and use that for syntax higlighting. In JS the magic syntactic pattern for triggering HTML syntax highlighting is:
In Python the magic syntactic pattern would be: My point in showing that JS counterexample was to demonstrate that the real reason people don't do that kind of thing isn't that they can't, it's that they like having syntax highlighting. That means the approach should work just as well in Python. This is the case even though the heuristic involved is very weak. Changing the name of the identifier or breaking into multiple expressions would be enough to break the heuristic in either language, which is why I think it's a really weak heuristic and dangerous pitfall for developers who might mistake the coloring for information about how the runtime sees that data (which is normally what syntax highlighting is for)Now, I'll just ignore that you're still deliberately misrepresenting me in the hopes of gaining some actual knowledge from this discussion - please show me: which editor supports syntax highlighting for the specific example you just mentioned? After all, that was the topic of discussion - not whether it's possible to delay "tagging", but whether it's easier to do syntax highlighting for JS template tags. Please show me an existing editor, IDE or git repo for a tool that would highlight your specific example based on the `html(...template)` call in line 4 (so no heuristics based on line 3). Surely you're not just throwing random examples at the wall to see what sticks, right? You've actually been following the discussion and are arguing in the context of it?
You can do that in python by accessing the `strings` and `values`, but I expect most cases will simply iterate the template, yielding a unified typed view of literal strings and interpolated values.
As for variables and arbitrary code/lambdas, yes: t-strings can do that, just like f-strings
I actually quite like the simplicity of this design over tagged literals in JS.
In other words, t-strings are basically f-strings where the final concatenation is delayed. And indeed, you can trivially implement f-strings using t-strings by performing a simple, non-escaped concatenation step: https://peps.python.org/pep-0750/#example-implementing-f-str...
This sounds like unnecessary fluff in what was supposed to be a simple language. I'm worried Python is turning into C++42 with 65535 ways to do one simple thing.
Why not just:
Nice and simple.Most DBs support parameterized queries which can be cached for performance. How do you pick out the parameters from that and replace those parts of the strings with the DB's parameter placeholders?
Looks very similar, but execution engine has access to all the individual parts, making it very easy to add placeholders such as: Or even (if the DB supports it), has access to the expressions inside the string and can use named parameters: That's really nice for debugging, depending on your DB engine.In every DB engine that supports it, parameterized SQL is even safer than escape syntaxes because parameters are passed in entirely different parts of the binary protocols and don't need to rely on just string manipulation to add escape sequences.
The "subsequent logic" has full access to the interpolation results and strings. Not only can it escape the results, it can do whatever it wants to them. It can also do whatever it wants to the strings, and then combine everything in any way it likes - it's not even necessary that the final result is a string.
name = "World"
template = t"Hello {(lambda: name)}"
This looks cool
This is of the category "things I wouldn't want to use even for the specific hyper niche things they're intended for". What even does a "t-string" represent? Because it's clearly not a string of any kind, it's a weird kind of function call notation. The programmer sees something that looks like string formatting, but the program executes some arbitrary procedure that might not return a string whatsoever.
The syntactic sugar of changing it from sql(t"...") doesn't seem particularly valuable. The novel thing about t-strings is that they change the parsing at compile-time.
It's valuable because:
- IDEs could then syntax-highlight SQL inside of SQL strings and HTML inside of HTML strings
- You can't accidentally pass an HTML string to your SQL library
There’s nothing stopping you from building a Python function that parses a string looking for {} and then searching globals for those variables. And you can extend that to also do some code execution and formatting.
To me the real sugar of f-strings is that the editor knows that it’s a template and not just a string. Expanding this to having SQL and regex syntax highlighting, linting and code formatting inside my Python code is a pretty cool prospect.
Your sql there would just be a function that receives the array of strings/values and returns whatever.
The concept of prefixes itself feels a little deviant from readable code that is close to human language -- which is the spirit of Python
Also, don’t get me started on g strings.
No
> They are just a special case of t strings.
Not really, because they produce a string right away instead of a template.
The only reason I could imagine, is if you are trying to protect developers from themselves, which kinda goes against the "we're all adults here" mentality that makes Python so great. I suppose it's easy enough to add that functionality, but come on.
The syntax is template literals, not just "tagged templates". Which is a huge difference: template literals still act as real strings. They don't need a tag prefix to work, you have the option to tag them if and when needed.
As far as I understand it, t-strings can't do that. They're not strings, and you can't even coerce them into strings, you have to run them through a processor before they become a string. So they're nothing like JS's template literals, they're syntactic sugar for forming "an instance of an object that needs to be passed into a function that returns a string".
So I don't look forward to folks preferring f-strings over t-strings even when they really shouldn't, simply because "having to constantly convert them from not-a-string to a string is a hassle". If only they'd worked like JS template literals.. that would have been fantastic.
t-strings are actually not strings, but Template objects, giving access to both the templating string and the parameters for processing. Sibling comments describe it as a custom .format implementation in that sense - it's f-string-like sugar where you're also allowed to take control of the .format function that it's sugar for.
Seems like a self selection which renders this meaningless, to some extent :/
t-strings are a different type (both static and dynamic), f-strings are not. So t-strings can be mandated at the API level, forcing the developer into "proper" usage.
That is, you need third-party tools to differentiate between
and That is not the case when it comes to t-strings, `some_call` can typecheck internally that it got a t-string, and reject regular strings entirely.Although some space probably needs to be made for composing t-strings together in case of e.g. runtime variation in items or their count. Facetting for instance. I don't know if that's a native affordance of t-strings.
And I love Python but, having been through 2->3 ( occasionally still going through it! ) whenever I see a new language feature my first thought is "Thank goodness it doesn't break everything that went before it".
I've been programming with Python since 2006, I think most of the systems were based on 2.4 at the time. I've been one of those who switched to Python 3 somewhat late, waiting for some major libraries to ship python 3 packages - celery and Twisted were one of the biggest holdouts - so I remember that the first project where all my dependencies were ready for python 3 was around 2015.
This is to say: even seasoned developers who were conservative around the migration have spent more time working with Python 3 than Python 2. There simply is no reason anymore to be talking about python 2.
Buuuttt, I'm so over the transition. It’s ancient now and I agree that we can stop fretting about it.
We are not completely Post Traumatic Python2 Stress yet, I am afraid.
Bad decisions can have looong-term repercussions.