Hands-On Reactive Programming with Python

The count operator

The count operator counts the number of items in the source observable that meet some criteria. The following figure shows the marble diagram of this operator:

Figure 9.37: The count operator

Its prototype is the following:

Observable.count(self, predicate=None)

Here, the predicate argument is a function that returns True if the item must be counted, or False otherwise.

Here is an example of the count operator:

numbers = Observable.from_([1, 2, 3, 4])numbers.count(lambda i: i > 2).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") ...