Re: [PATCH v7 25/33] iotests.py: VM: add own __enter__ method

[John Snow]

On Wed, Aug 4, 2021 at 5:39 AM Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com> wrote:

In superclass __enter__ method is defined with return value type hint
'QEMUMachine'. So, mypy thinks that return value of VM.__enter__ is
QEMUMachine. Let's redefine __enter__ in VM class, to give it correct
type hint.

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>
---
 tests/qemu-iotests/iotests.py | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/tests/qemu-iotests/iotests.py b/tests/qemu-iotests/iotests.py
index 89663dac06..025e288ddd 100644
--- a/tests/qemu-iotests/iotests.py
+++ b/tests/qemu-iotests/iotests.py
@@ -568,6 +568,10 @@ def remote_filename(path):
 class VM(qtest.QEMUQtestMachine):
     '''A QEMU VM'''

+    # Redefine __enter__ with proper type hint
+    def __enter__(self) -> 'VM':
+        return self
+
     def __init__(self, path_suffix=''):
         name = "qemu%s-%d" % (path_suffix, os.getpid())
         super().__init__(qemu_prog, qemu_opts, name=name,
--
2.29.2

First and foremost:

Reviewed-by: John Snow <jsnow@redhat.com>

Acked-by: John Snow <jsnow@redhat.com>

A more durable approach might be to annotate QEMUMachine differently such that subclasses get the right types automatically. See if this following snippet works instead of adding a new __enter__ method.

diff --git a/python/qemu/machine/machine.py b/python/qemu/machine/machine.py
index 971ed7e8c6a..2e410103569 100644
--- a/python/qemu/machine/machine.py
+++ b/python/qemu/machine/machine.py
@@ -36,6 +36,7 @@
     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.
@@ -166,7 +170,7 @@ def __init__(self,
         self._remove_files: List[str] = []
         self._user_killed = False
 
-    def __enter__(self) -> 'QEMUMachine':
+    def __enter__(self: _T) -> _T:
         return self
 
     def __exit__(self,
@@ -182,8 +186,8 @@ def add_monitor_null(self) -> None:
         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
         """