Python State Machines

State machines allow you to describe the high level logic of your program while ignoring low level implementation details. They are especially useful for modeling event-driven systems.

Theory and Concepts

Statecharts

Here is the original paper written by David Harel in 1986. This gave birth to the UML state diagrams we have today. Read the full article

UML State Diagrams

This Wikipedia article explains the basics of Events, States, Guards, and Actions. Read this if you need to get up to speed on basic concepts and terminology. Read the full article

State Diagram Crash Course

This 30 page whitepaper makes a strong argument for using state machines instead of giant if-else statements. It uses the Visual Basic calculator program to illustrate how state machines can simplify your code and eliminate bugs. Read the full article

Videos

UML State Diagrams

Derek Banas teaches you the UML notation in this 13 minute YouTube video. Watch the video

Coding a State Machine by Hand

You probably don't want to do this. Watch the video

Libraries and Tools

pystatemachine 1.2

A clever idea. This package uses Python @decorators to turn any class into a state machine. Read the full article

State Machine Compiler (SMC)

Writing state machine code is dull, repetitive, and error prone. Let the computer do it for you. This tool generates Python code from a high-level description of your state machine. Read the full article