python/qemu: Adjust traceback typing

mypy considers it incorrect to use `bool` to statically return false,
because it will assume that it could conceivably return True, and gives
different analysis in that case. Use a None return to achieve the same
effect, but make mypy happy.

Note: Pylint considers function signatures as code that might trip the
duplicate-code checker. I'd rather not disable this as it does not
trigger often in practice, so I'm disabling it as a one-off and filed a
change request; see https://github.com/PyCQA/pylint/issues/3619

Signed-off-by: John Snow <jsnow@redhat.com>
Acked-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Message-Id: <20200514055403.18902-14-jsnow@redhat.com>
Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>

1 files changed, 6 insertions, 2 deletions

diff --git a/python/qemu/machine.py b/python/qemu/machine.py
index 95a20a17f9..041c615052 100644
--- a/python/qemu/machine.py
+++ b/python/qemu/machine.py
@@ -24,6 +24,8 @@ import subprocess
 import shutil
 import socket
 import tempfile
+from typing import Optional, Type
+from types import TracebackType
 
 from . import qmp
 
@@ -124,9 +126,11 @@ class QEMUMachine:
     def __enter__(self):
         return self
 
-    def __exit__(self, exc_type, exc_val, exc_tb):
+    def __exit__(self,
+                 exc_type: Optional[Type[BaseException]],
+                 exc_val: Optional[BaseException],
+                 exc_tb: Optional[TracebackType]) -> None:
         self.shutdown()
-        return False
 
     def add_monitor_null(self):
         """