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>

python/qemu/qmp/error.py

@@ -44,7 +44,10 @@ class ProtocolError(QMPError):
 
     :param error_message: Human-readable string describing the error.
     """
-    def __init__(self, error_message: str):
-        super().__init__(error_message)
+    def __init__(self, error_message: str, *args: object):
+        super().__init__(error_message, *args)
         #: Human-readable error message, without any prefix.
         self.error_message: str = error_message
+
+    def __str__(self) -> str:
+        return self.error_message

python/qemu/qmp/message.py

@@ -178,15 +178,15 @@ class DeserializationError(ProtocolError):
     :param raw: The raw `bytes` that prompted the failure.
     """
     def __init__(self, error_message: str, raw: bytes):
-        super().__init__(error_message)
+        super().__init__(error_message, raw)
         #: The raw `bytes` that were not understood as JSON.
         self.raw: bytes = raw
 
     def __str__(self) -> str:
-        return "\n".join([
+        return "\n".join((
             super().__str__(),
             f"  raw bytes were: {str(self.raw)}",
-        ])
+        ))
 
 
 class UnexpectedTypeError(ProtocolError):
@@ -197,13 +197,13 @@ class UnexpectedTypeError(ProtocolError):
     :param value: The deserialized JSON value that wasn't an object.
     """
     def __init__(self, error_message: str, value: object):
-        super().__init__(error_message)
+        super().__init__(error_message, value)
         #: The JSON value that was expected to be an object.
         self.value: object = value
 
     def __str__(self) -> str:
         strval = json.dumps(self.value, indent=2)
-        return "\n".join([
+        return "\n".join((
             super().__str__(),
             f"  json value was: {strval}",
-        ])
+        ))

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
 

python/qemu/qmp/qmp_client.py

@@ -41,7 +41,7 @@ class _WrappedProtocolError(ProtocolError):
     :param exc: The root-cause exception.
     """
     def __init__(self, error_message: str, exc: Exception):
-        super().__init__(error_message)
+        super().__init__(error_message, exc)
         self.exc = exc
 
     def __str__(self) -> str:
@@ -76,15 +76,21 @@ class ExecuteError(QMPError):
     """
     def __init__(self, error_response: ErrorResponse,
                  sent: Message, received: Message):
-        super().__init__(error_response.error.desc)
+        super().__init__(error_response, sent, received)
         #: The sent `Message` that caused the failure
         self.sent: Message = sent
         #: The received `Message` that indicated failure
         self.received: Message = received
         #: The parsed error response
         self.error: ErrorResponse = error_response
-        #: The QMP error class
-        self.error_class: str = error_response.error.class_
+
+    @property
+    def error_class(self) -> str:
+        """The QMP error class"""
+        return self.error.error.class_
+
+    def __str__(self) -> str:
+        return self.error.error.desc
 
 
 class ExecInterruptedError(QMPError):
@@ -110,8 +116,8 @@ class _MsgProtocolError(ProtocolError):
     :param error_message: Human-readable string describing the error.
     :param msg: The QMP `Message` that caused the error.
     """
-    def __init__(self, error_message: str, msg: Message):
-        super().__init__(error_message)
+    def __init__(self, error_message: str, msg: Message, *args: object):
+        super().__init__(error_message, msg, *args)
         #: The received `Message` that caused the error.
         self.msg: Message = msg
 
@@ -150,7 +156,7 @@ class BadReplyError(_MsgProtocolError):
     :param sent: The message that was sent that prompted the error.
     """
     def __init__(self, error_message: str, msg: Message, sent: Message):
-        super().__init__(error_message, msg)
+        super().__init__(error_message, msg, sent)
         #: The sent `Message` that caused the failure
         self.sent = sent