On 30 November 2017 at 22:38, Ilya Kulakov
A very rough implementation:
typing.py:
class _GenericMetaNoop(type): def __getitem__(self, params): return self
class _GenericNoop(metaclass=_GenericMetaNoop) pass
GenericStub = Generic if TYPE_CHECKING else _GenericNoop
elsewhere.py:
import typing
T = typing.TypeVar('T')
class MyClass(typing.GenericStub[T]): pass
OK, I see. Note that all type checkers known to me never actually read content of typing.py (it is always heavily special cased). Therefore, one can safely write `GenericStub = _GenericNoop`. Anyway, my expectation is that going along this way (i.e. removing all runtime API apart from a necessary minimum) will give a minor speed-up as compared to PEP 560 at the cost of a breaking change (even for small number of developers). PEP 560 already gives overhead of 80% as compared to normal classes in worst case scenario (empty body with a single generic base). This is actually less than for ABCs (they can give up to 120% in worst case scenario). Moreover, performance is not a single motivation for PEP 560, there are other arguments such as metaclass conflicts which will not be solved without the machinery proposed by the PEP. -- Ivan