> This is loosely the same idea that drives React, ObservableHQ, Kafka, and other event-streaming architectures, but I first encountered this ~15 years ago at a bank.

See also the "observer pattern" [0]. It's a fun exercise to implement a reactive system in Python using the descriptor protocol [1]. IPython's traitlets library is an example of this in the wild [2].

[0]: https://en.wikipedia.org/wiki/Observer_pattern

[1]: https://docs.python.org/3/howto/descriptor.html

[2]: https://github.com/ipython/traitlets