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

[John Snow <jsnow@redhat.com>]

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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
         """

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