The distinct operator returns only unique items from its source observable. The following figure shows its marble diagram:

Its prototype is the following:

Observable.distinct(self, key_selector=None, comparer=None)

Here, key_selector is a function that returns a key from each item. The default value uses the item as a key. The comparer parameter is a function used to compare two keys. Its default value uses the equality operator. Both parameters are optional.

Here is an example of the distinct operator:

numbers = Observable.from_([1, 2, 1, 3, 3, 2, 4, 5])
numbers.distinct().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")
)

This example gives the following result:

on_next 1
on_next 2
on_next 3
on_next 4
on_next 5
on_completed