Add BaseRequestHandler instance attributes

From the BaseRequestHandler documentation:

    handle()

    This function must do all the work required to service a request.
    The default implementation does nothing. Several instance attributes
    are available to it; the request is available as self.request; the
    client address as self.client_address; and the server instance as
    self.server, in case it needs access to per-server information.

    The type of self.request is different for datagram or stream
    services. For stream services, self.request is a socket object;
    for datagram services, self.request is a pair of string and
    socket.

Author: Jakub Stasiak

stdlib/3/socketserver.pyi

@@ -1,6 +1,6 @@
 # Stubs for socketserver
 
-from typing import BinaryIO, Optional, Tuple
+from typing import BinaryIO, Generic, Optional, Tuple, TypeVar, Union
 from socket import SocketType
 import sys
 import types
@@ -68,15 +68,23 @@ class ForkingUDPServer(ForkingMixIn, UDPServer): ...
 class ThreadingTCPServer(ThreadingMixIn, TCPServer): ...
 class ThreadingUDPServer(ThreadingMixIn, UDPServer): ...
 
-class BaseRequestHandler:
+
+_RequestT = TypeVar('_RequestT', SocketType, Tuple[bytes, SocketType])
+# str in case of Unix domain socket
+_AddressT = TypeVar('_AddressT', Tuple[str, int], str)
+
+class BaseRequestHandler(Generic[_RequestT, _AddressT]):
+    request = ...  # type: _RequestT
+    client_address = ...  # type: _AddressT
+    server = ...  # type: BaseServer
     def setup(self) -> None: ...
     def handle(self) -> None: ...
     def finish(self) -> None: ...
 
-class StreamRequestHandler(BaseRequestHandler):
+class StreamRequestHandler(BaseRequestHandler[SocketType, _AddressT]):
     rfile = ...  # type: BinaryIO
     wfile = ...  # type: BinaryIO
 
-class DatagramRequestHandler(BaseRequestHandler):
+class DatagramRequestHandler(BaseRequestHandler[Tuple[bytes, SockeType], _AddressT]):
     rfile = ...  # type: BinaryIO
     wfile = ...  # type: BinaryIO