Breaking it down

In the preceding code, we kept the same observable that we implemented in the previous example, but you'll notice one key difference. We no longer have this rather verbose StockObserver class definition and have replaced it with a far more terse one liner, which features all of the same functionality:

source.subscribe(lambda value: print("Received Instruction to buy {0}".format(value)))

In this particular example, we minimized our code base and made our code more maintainable as we don't have to pour over an entire class definition to see what's happening. However, it should be noted that while this was advantageous here, trying to cram all of your code into a single lambda expression could actually hamper your code's readability and make maintenance work and bug fixes a nightmare.