The amb operator emits items from the first observable of two that emits an item first. The following figure shows the marble diagram of this operator:

Its prototype is the following:

Observable.amb(self, right_source)

The right_source parameter is the second observable to watch.

Here is an example of the amb operator:

first = Subject()
second = Subject()

first.amb(second).subscribe(
    on_next = lambda i: print("on_next {}".format(i)),
    on_error = lambda e: print("on_error: {}".format(e)),
    on_completed = lambda: print("on_completed")
)
    
first.on_next(1)
second.on_next(2)
first.on_completed()

In this example, the first observable emits an item before the second observable.

This example gives the following result:

on_next 1
on_completed