python: backport 'Change error classes to have better repr methods'

By passing all of the arguments to the base class and overriding the
__str__ method when we want a different "human readable" message that
isn't just printing the list of arguments, we can ensure that all custom
error classes have a reasonable __repr__ implementation.

In the case of ExecuteError, the pseudo-field that isn't actually
correlated to an input argument can be re-imagined as a read-only
property; this forces consistency in the class and makes the repr output
more obviously correct.

Signed-off-by: John Snow <jsnow@redhat.com>
cherry picked from commit python-qemu-qmp@afdb7893f3b34212da4259b7202973f9a8cb85b3
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>

1 files changed, 5 insertions, 2 deletions

diff --git a/python/qemu/qmp/protocol.py b/python/qemu/qmp/protocol.py
index a4ffdfa..86e5888 100644
--- a/python/qemu/qmp/protocol.py
+++ b/python/qemu/qmp/protocol.py
@@ -80,7 +80,7 @@ class ConnectError(QMPError):
     :param exc: The root-cause exception.
     """
     def __init__(self, error_message: str, exc: Exception):
-        super().__init__(error_message)
+        super().__init__(error_message, exc)
         #: Human-readable error string
         self.error_message: str = error_message
         #: Wrapped root cause exception
@@ -108,11 +108,14 @@ class StateError(QMPError):
     """
     def __init__(self, error_message: str,
                  state: Runstate, required: Runstate):
-        super().__init__(error_message)
+        super().__init__(error_message, state, required)
         self.error_message = error_message
         self.state = state
         self.required = required
 
+    def __str__(self) -> str:
+        return self.error_message
+
 
 F = TypeVar('F', bound=Callable[..., Any])  # pylint: disable=invalid-name