python:QEMUMachine: template typing for self returning methods

mypy thinks that return value of these methods in subclusses is
QEMUMachine, which is wrong. So, make typing smarter.

Suggested-by: John Snow <jsnow@redhat.com>
Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Message-Id: <20210824083856.17408-26-vsementsov@virtuozzo.com>
Reviewed-by: Hanna Reitz <hreitz@redhat.com>
Signed-off-by: Hanna Reitz <hreitz@redhat.com>

diff --git a/python/qemu/machine/machine.py b/python/qemu/machine/machine.py
index 6ec18570d90300bec897e36d2ace99028218147e..a7081b18452b446320c96c995fe5e78a097a69b3 100644 (file)
--- a/python/qemu/machine/machine.py
+++ b/python/qemu/machine/machine.py
@@ -36,6 +36,7 @@ from typing import (
     Sequence,
     Tuple,
     Type,
+    TypeVar,
 )
 
 from qemu.qmp import (  # pylint: disable=import-error
@@ -73,6 +74,9 @@ class AbnormalShutdown(QEMUMachineError):
     """
 
 
+_T = TypeVar('_T', bound='QEMUMachine')
+
+
 class QEMUMachine:
     """
     A QEMU VM.
@@ -169,7 +173,7 @@ class QEMUMachine:
         self._remove_files: List[str] = []
         self._user_killed = False
 
-    def __enter__(self) -> 'QEMUMachine':
+    def __enter__(self: _T) -> _T:
         return self
 
     def __exit__(self,
@@ -185,8 +189,8 @@ class QEMUMachine:
         self._args.append('-monitor')
         self._args.append('null')
 
-    def add_fd(self, fd: int, fdset: int,
-               opaque: str, opts: str = '') -> 'QEMUMachine':
+    def add_fd(self: _T, fd: int, fdset: int,
+               opaque: str, opts: str = '') -> _T:
         """
         Pass a file descriptor to the VM
         """