I think it would be useful to compile a table of various ways one can use
typevars to show the analogous syntax using each of the proposals. E.g.
# Classic
T = TypeVar("T")
class C(Generic[T]):
def f(self, arg: T) -> T: ...
# Angle brackets
class C<T>:
def f(self, arg: T) -> T: ...
# Square brackets
class C[T]:
def f(self, arg: T) -> T: ...
# Decorator
@typevar("T")
class C:
def f(self, arg: T) -> T: ...
Include examples using variance (could we use +T, -T for covariant,
contravariant?), bounds and constraints. Show generic functions as well as
classes. Go wild.
When using the decorator syntax, I have a question: how would the
implementation of `typevar` insert the name "T" into the surrounding scope
so that it can be used inside the class or function? sys._getframe()?
(Urgh.)
On Mon, Mar 14, 2022 at 8:05 AM Sebastian Rittau
Am 14.03.22 um 15:51 schrieb Sergei Lebedev:
class C[T, S]: def foo[R=int](self) -> R: pass
Could you clarify what the "=int" part stands for?
A type var default (not currently supported by type vars).
Some ideas how we could express upper bounds, constraints, and variance: [...]
Wdyt about <= for defining an upper bound and +/- for variance annotations? IIRC both are used at least in Scala and OCaml has +/- for specifying variance and for polymorphic variants https://ocaml.org/manual/polyvariant.html.
This could work, but I'm not too fond of using too many punctuation characters. Python has always been the antithesis to "line-noise" Perl, and I think "key words" (not necessarily "keywords" from a parser perspective) are more readable and obvious.
* Could we make it work for ParamSpecs?
This is one more reason a decorator syntax could be better:
@paramspec("P") def foo(*args: P.args, **kwargs: P.kwargs) -> None: ... - Sebastian _______________________________________________ Typing-sig mailing list -- typing-sig@python.org To unsubscribe send an email to typing-sig-leave@python.org https://mail.python.org/mailman3/lists/typing-sig.python.org/ Member address: guido@python.org
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