Hands-On Reactive Programming with Python

Chapter 4

How do you create an observable that emits only one value?

The operator just emits a single item and then completes. The following code snippet returns an observable that emits a string item and then completes:

single_item = Observable.just("a single item")

How do you create an observable that emits one item from each line of a text file?

This requires an observable with some specific code logic in it, so it must be implemented with the create operator. A possible implementation of this observable is as follows:

def create_line_observable(filename):    def on_subscribe(observer):        with open('filename') as f:            lines = f.readlines()            for line in lines:                observer.on_next(line)        observer.on_completed() return Observable.create(on_subscribe) ...