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Chapter 10. Error handling
Errors in AMQ Python can be handled in two different ways:
- Catching exceptions
- Overriding event-handling functions to intercept AMQP protocol or connection errors
10.1. Catching exceptions
All of the exceptions that AMQ Python throws inherit from the ProtonException class, which in turn inherits from the Python Exception class.
The following example illustrates how to catch any exception thrown from AMQ Python:
Example: API-specific exception handling
try:
# Something that might throw an exception
except ProtonException as e:
# Handle Proton-specific problems here
except Exception as e:
# Handle more general problems here
}
If you do not require API-specific exception handling, you only need to catch Exception, since ProtonException inherits from it.
10.2. Handling connection and protocol errors
You can handle protocol-level errors by overriding the following messaging_handler methods:
-
on_transport_error(event) -
on_connection_error(event) -
on_session_error(event) -
on_link_error(event)
These event-handling functions are called whenever there is an error condition with the specific object that is in the event. After calling the error handler, the appropriate close handler is also called.
Because the close handlers are called in the event of any error, only the error itself needs to be handled within the error handler. Resource cleanup can be managed by close handlers. If there is no error handling that is specific to a particular object, it is typical to use the general on_error handler and not have a more specific handler.
When reconnect is enabled and the remote server closes a connection with the amqp:connection:forced condition, the client does not treat it as an error and thus does not fire the on_connection_error handler. The client instead begins the reconnection process.
