machine: type-annotate the Timeout class

This is not as nice as it could be: my first choice here would have been
to eliminate the dependency inversion (that Timeout knows what a
"machine" is) and avoid the cyclic import, but there are external users
of this API which depend on the `machine=` kwarg, so we need to keep
it for now.

Author: allisonkarlitskaya

machine/machine_core/timeout.py

@@ -16,13 +16,17 @@
 # along with Cockpit; If not, see <http://www.gnu.org/licenses/>.
 
 import signal
+import typing
+
+if typing.TYPE_CHECKING:
+    from .ssh_connection import SSHConnection
 
 
 class Timeout:
     """ Add a timeout to an operation
         Specify machine to ensure that a machine's ssh operations are canceled when the timer expires.
     """
-    def __init__(self, seconds=1, error_message='Timeout', machine=None):
+    def __init__(self, seconds: int = 1, error_message: str = 'Timeout', machine: 'SSHConnection | None' = None):
         if signal.getsignal(signal.SIGALRM) != signal.SIG_DFL:
             # there is already a different Timeout active
             self.seconds = None
@@ -32,20 +36,20 @@ def __init__(self, seconds=1, error_message='Timeout', machine=None):
         self.error_message = error_message
         self.machine = machine
 
-    def handle_timeout(self, signum, frame):
+    def handle_timeout(self, _signum: int, _frame: object) -> None:
         if self.machine:
             if self.machine.ssh_process:
                 self.machine.ssh_process.terminate()
             self.machine.disconnect()
 
         raise RuntimeError(self.error_message)
 
-    def __enter__(self):
+    def __enter__(self) -> None:
         if self.seconds:
             signal.signal(signal.SIGALRM, self.handle_timeout)
             signal.alarm(self.seconds)
 
-    def __exit__(self, _type, value, traceback):
+    def __exit__(self, _type: object, _value: object, _traceback: object) -> None:
         if self.seconds:
             signal.alarm(0)
             signal.signal(signal.SIGALRM, signal.SIG_DFL)