`isinstance` check with nested `Protocol`.

isinstance(obj, ProtocolSubclass) only checks the the existence of ProtocolSubclass's methods on obj and not the type signature. To provide deeper checks, maybe isinstance could check attributes/methods on ProtocolSubclass that are themselves a Protocol.

A small example showing the change in behavior:

@runtime_checkable
class FooLike(Protocol):
    attr: str

@runtime_checkable
class BarLike(Protocol):
    attr: FooLike

@dataclass
class Foo:
    attr: str = "test"

@dataclass
class Bar:
    attr: Foo

foo = Foo()
bar = Bar(foo)

# No change in current behavior
assert isinstance(foo, FooLike)  # passes
assert isinstance(bar, BarLike)  # passes
assert isinstance(bar, FooLike)  # passes

# Change in behavior
assert not isinstance(foo, BarLike)  # NOT because `BarLike.attr` should be `FooLike` and `foo.attr` is not

Commencez par le comportement à l’exécution de isinstance(obj, ProtocolSubclass) et les exemples de @runtime_checkable Protocol du rapport. Comparez les vérifications superficielles actuelles de l’existence des attributs avec le comportement imbriqué de Protocol demandé, puis utilisez les assertions de l’exemple pour définir l’achèvement.