reactive programming introduction publishedthen the application must update the value of the trade within the table such an application can be described as being reactive reactive programming is programming style (typically supported by librariesthat allows code to be written that follow the ideas of reactive systems of course just because part of an application uses reactive programming library does not make the whole application reactiveindeed it may only be necessary for part of an application to exhibit reactive behaviour the reactivex project reactivex is the best known implementation of the reactive programming paradigm reactivex is based on the observer-observable design pattern however it is an extension to this design pattern as it extends the pattern such that the approach supports sequences of data and/or events and adds operators that allow developers to compose sequences together declaratively while abstracting away concerns associated with low-level threadssynchronisationconcurrent data structures and non-blocking / the reactivex project has implementations for many languages including rxjavarxscala and rxpythis last is the version we are looking at as it is for the python language rxpy is described asa library for composing asynchronous and event-based programs using observable collections and query operator functions in python the observer pattern the observer pattern is one of the gang of four set of design patterns the gang of four patterns (as originally described in gamma et al are so called because this book on design patterns was written by four very famous authors namelyerich gammarichard helmralph johnson and john vlissides the observer pattern provides way of ensuring that set of objects is notified whenever the state of another object changes it has been widely used in number of languages (such as smalltalk and javaand can also be used with python the intent of the observer pattern is to manage one to many relationship between an object and those objects interested in the stateand in particular state changesof that object thus when the objectsstate changesthe interested (dependentobjects are notified of that change and can take whatever action is appropriate