Now let's see how to use Subject to implement the directed cyclic graph of the previous example. Instead of referencing the a_out variable directly, Subject is used:

b_in_proxy = Subject()
b_out = component_b(b_in_proxy)
a_out = component_a(b_out)
a_out.subscribe(b_in_proxy)

The complete code of this example is available at: https://github.com/PacktPublishing/Hands-On-Reactive-Programming-with-Python in the cycle_subject.py script.