Jim Baker's draft PEP gives runtime behavior to tagged strings. I agree it would all be pointless if it's just hints to an editor. Sorry, I again don't have a handy link to his PEP. But it's similar in spirit to PEP 501. Eric On 12/22/2022 2:36 PM, Joao S. O. Bueno wrote:
I am not enthusiastic about this idea at all: as I perceive it it is an IDE problem, external to the language, and should be resolved there - maybe with a recommendation PEP.
But on the other hand, I had seem tens of e-mails discussing string-subclassing, so that annotations could suffice as a hint to inner-string highlighting - and then: subclassing is not really needed at all: Maybe we can allow string tagging in annotations by using `str['html']`, "str['css']" and so on. (the typing module even could take no-op names such as "html", "css", etc... to mean those without any other signs, so stuff could be annotated like `template: html = "xxxx"` which the the same typing machinery that makes things like `TypedDict`. `Required`, etc... work would present these as plain "str" to the runtime, while allowing any tooling to perceive it as a specialized class.
In other words, one could then either write:
mytemplate: str['html'] = "<html> ....</html>"
Or
from typing import html mytemplate: html = ...
(the former way could be used for arbitrary tagging as proposed by the O.P. , and it would be trivial to add a "register" function to declaratively create new tags at static-analysis time.
This syntax has the benefits that static type checkers can take full-beneffit of the string subtypes, correctly pointing out when a "CSS" string is passed as an argument that should contain "HTML", with no drawbacks, no syntax changes, and no backwards compatibility breaks.
On Thu, Dec 22, 2022 at 1:42 AM Christopher Barker <pythonchb@gmail.com> wrote:
On Wed, Dec 21, 2022 at 9:35 AM Chris Angelico <rosuav@gmail.com> wrote:
>From the look of things, PyUnicode_Join (the internal function that handles str.join()) uses a lot of "reaching into the data structure" operations for efficiency. It uses PyUnicode_Check (aka "isinstance(x, str)") rather than PyUnicode_CheckExact (aka "type(x) is str") and then proceeds to cast the pointer and directly inspect its members.
As such, I don't think UserString can ever truly be a str,
I had figured subclasses of str wouldn’t be full players in the C code — but join() us pretty fundamental:-(
-CHB -- Christopher Barker, PhD (Chris)
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