On Fri, Apr 16, 2021 at 8:27 AM Inada Naoki <songofaca...@gmail.com> wrote:
> After PEP 563, only `'List[int]'` is practical so we can stop > supporting `List["int"]` and others at some point. > There's a lot of code written before PEP 563 was available (and code that needs to support earlier Python versions) that uses string literal quoting in various places. If Python stops supporting List["X"], it will be a significant backward compatibility break. Some of these string literal escapes are made unnecessary by PEP 563, but there are still cases where string literals are needed that neither PEP 563 nor PEP 649 address. Examples include type aliases, type variable definitions and base classes, but there are others [1]. These aren't evaluated in a type annotation context, so manual string literal escaping would still be needed. > So playing with runtime type will become easier in the future. > > Am I wrong? > In some cases things will become easier, but other common use cases still seem to be unresolved. I haven't seen any proposal that can completely replace all uses of string literal escapes. I guess one option would be to only allow string literal escaping to be used outside type annotations in the future. I think that this could be feasible with a suitable deprecation period. Also, the use of "if TYPE_CHECKING" breaks the runtime use of annotations. PEP 563 and PEP 649 reduce the need for string literal escaping in this use case, but it mostly helps static type checkers. This is pretty common in codebases that use static type checking. My main issue with PEP 649 is that it only addresses a subset of remaining issues, i.e. it doesn't go far enough. It's also not clear to me if PEP 649 (or PEP 563) can be extended to cover the remaining runtime issues, or if we'd need a *third* approach to solve them. Jukka [1] https://www.python.org/dev/peps/pep-0563/#forward-references
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