The catch_exception operator allows us to catch any error coming from its source observable and to continue to emit items. When the error occurs in the source observable, the catch_exception operator continues the sequence with another sequence of items. Its marble diagram is shown in the following figure:

Its prototype is as follows:

Observable.catch_exception(self, second=None, handler=None):

The optional second argument is either an observable to chain when an error occurs in the source observable or a function that returns an observable. The optional handler argument is an exception handler that must return a future. This future will be wrapped in an observable. Only one of the two arguments must be used. The following is an example of this operator:

err = Observable.throw("error!")
err.catch_exception(lambda e: Observable.from_([1,2,3])) 
    .subscribe(
        on_next=lambda i: print("item: {}".format(i)),
        on_error=lambda e: print("error: {}".format(e)),
        on_completed=lambda: print("completed")
    )

The following is the output of this example:

item: 1
item: 2
item: 3
completed

The error has been caught correctly and has been replaced with another observable.