stdlib: add __slots__ (#14611)

stdlib/asyncio/protocols.pyi

@@ -6,21 +6,26 @@ from typing import Any
 __all__ = ("BaseProtocol", "Protocol", "DatagramProtocol", "SubprocessProtocol", "BufferedProtocol")
 
 class BaseProtocol:
+    __slots__ = ()
     def connection_made(self, transport: transports.BaseTransport) -> None: ...
     def connection_lost(self, exc: Exception | None) -> None: ...
     def pause_writing(self) -> None: ...
     def resume_writing(self) -> None: ...
 
 class Protocol(BaseProtocol):
+    # Need annotation or mypy will complain about 'Cannot determine type of "__slots__" in base class'
+    __slots__: tuple[()] = ()
     def data_received(self, data: bytes) -> None: ...
     def eof_received(self) -> bool | None: ...
 
 class BufferedProtocol(BaseProtocol):
+    __slots__ = ()
     def get_buffer(self, sizehint: int) -> ReadableBuffer: ...
     def buffer_updated(self, nbytes: int) -> None: ...
     def eof_received(self) -> bool | None: ...
 
 class DatagramProtocol(BaseProtocol):
+    __slots__ = ()
     def connection_made(self, transport: transports.DatagramTransport) -> None: ...  # type: ignore[override]
     # addr can be a tuple[int, int] for some unusual protocols like socket.AF_NETLINK.
     # Use tuple[str | Any, int] to not cause typechecking issues on most usual cases.
@@ -30,6 +35,7 @@ class DatagramProtocol(BaseProtocol):
     def error_received(self, exc: Exception) -> None: ...
 
 class SubprocessProtocol(BaseProtocol):
+    __slots__: tuple[()] = ()
     def pipe_data_received(self, fd: int, data: bytes) -> None: ...
     def pipe_connection_lost(self, fd: int, exc: Exception | None) -> None: ...
     def process_exited(self) -> None: ...