Deprecated since 3.15, removed in 3.20. It is deprecated to call isinstance() and issubclass() checks on protocol classes that were not explicitly decorated with runtime_checkable() but that inherit from a runtime-checkable protocol class. This will throw a TypeError in Python 3.20.
Base class for protocol classes.
Protocol classes are defined as::
class Proto(Protocol):
def meth(self) -> int:
...
Such classes are primarily used with static type checkers that recognize
structural subtyping (static duck-typing).
For example::
class C:
def meth(self) -> int:
return 0
def func(x: Proto) -> int:
return x.meth()
func(C()) # Passes static type check
See PEP 544 for details. Protocol classes decorated with
@typing.runtime_checkable act as simple-minded runtime protocols that check
only the presence of given attributes, ignoring their type signatures.
Protocol classes can be generic, they are defined as::
class GenProto[T](Protocol):
def meth(self) -> T:
...