Re: [PATCH v3 12/16] python/machine.py: Add _qmp access shim

[Philippe Mathieu-Daudé]

On 6/4/20 10:22 PM, John Snow wrote:
> Like many other Optional[] types, it's not always a given that this
> object will be set. Wrap it in a type-shim that raises a meaningful
> error and will always return a concrete type.
> 
> Signed-off-by: John Snow <jsnow@redhat.com>
> ---
>  python/qemu/machine.py | 12 +++++++++---
>  1 file changed, 9 insertions(+), 3 deletions(-)
> 
> diff --git a/python/qemu/machine.py b/python/qemu/machine.py
> index d8289936816..a451f9000d6 100644
> --- a/python/qemu/machine.py
> +++ b/python/qemu/machine.py
> @@ -118,7 +118,7 @@ def __init__(self, binary, args=None, wrapper=None, 
> name=None,
>          self._events = []
>          self._iolog = None
>          self._qmp_set = True   # Enable QMP monitor by default.
> -        self._qmp = None
> +        self._qmp_connection: Optional[qmp.QEMUMonitorProtocol] = None
>          self._qemu_full_args = None
>          self._temp_dir = None
>          self._launched = False
> @@ -285,7 +285,7 @@ def _pre_launch(self):
>              if self._remove_monitor_sockfile:
>                  assert isinstance(self._monitor_address, str)
>                  self._remove_files.append(self._monitor_address)
> -            self._qmp = qmp.QEMUMonitorProtocol(
> +            self._qmp_connection = qmp.QEMUMonitorProtocol(
>                  self._monitor_address,
>                  server=True,
>                  nickname=self._name
> @@ -455,7 +455,13 @@ def set_qmp_monitor(self, enabled=True):
>              self._qmp_set = True
>          else:
>              self._qmp_set = False
> -            self._qmp = None
> +            self._qmp_connection = None
> +
> +    @property
> +    def _qmp(self) -> qmp.QEMUMonitorProtocol:
> +        if self._qmp_connection is None:
> +            raise QEMUMachineError("Attempt to access QMP with no 
> connection")
> +        return self._qmp_connection
>  
>      @classmethod
>      def _qmp_args(cls, _conv_keys: bool = True, **args: Any) -> Dict[str, 
> Any]:
> 

This patch breaks the EmptyCPUModel test:

(043/101) tests/acceptance/empty_cpu_model.py:EmptyCPUModel.test:
ERROR: Attempt to access QMP with no connection (0.03 s)