Software Patterns

Event Sourcing with John Bywater - Episode 131

Summary

The way that your application handles data and the way that it is represented in your database don’t always match, leading to a lot of brittle abstractions to reconcile the two. In order to reduce that friction, instead of overwriting the state of your application on every change you can log all of the events that take place and then render the current state from that sequence of events. John Bywater joins me this week to discuss his work on the Event Sourcing library, why you might want to use it in your applications, and how it can change the way that you think about your data.

Preface

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  • Your host as usual is Tobias Macey and today I’m interviewing John Bywater about event sourcing, an architectural approach to make your data layer easier to scale and maintain.

Interview

  • Introductions
  • How did you get introduced to Python?
  • Can you start by describing the concept of event sourcing and the benefits that it provides?
  • What is the event sourcing library and what was your reason for starting it?
  • What are some of the reasons that someone might not want to implement an event sourcing approach in their persistence layer?
  • Given that you are storing a record for each event that occurs on a domain object, how does that affect the amount of storage necessary to support an event sourced application?
  • What is the impact on performance and latency from an end user perspective when the application is using event sourcing to render the current state of the system?
  • What does the internal architecture and design of your library look like and how has that evolved over time?
  • In the case where events are delivered out of order, how can you ensure that the present view of an object is reflected accurately?
  • For someone who wants to incorporate an event sourcing design into an existing application, how would they do that?
  • How do you manage schema changes in your domain model when you need to reconstruct present state from the beginning of an objects event sequence?
  • What are some of the most interesting uses of event sourcing that you have seen?
  • What are some of the features or improvements that you have planned for the future of you event sourcing library?

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The intro and outro music is from Requiem for a Fish The Freak Fandango Orchestra / CC BY-SA

Automat State Machines with Glyph Lefkowitz - Episode 116

Summary

The venerable ‘if’ statement is a cornerstone of program flow and busines logic, but sometimes it can grow unwieldy and lead to unmaintainable software. One alternative that can result in cleaner and easier to understand code is a state machine. This week Glyph explains how Automat was created and how it has been used to upgrade portions of the Twisted project.

Preface

  • Hello and welcome to Podcast.__init__, the podcast about Python and the people who make it great.
  • I would like to thank everyone who supports us on Patreon. Your contributions help to make the show sustainable.
  • When you’re ready to launch your next project you’ll need somewhere to deploy it. Check out Linode at www.podastinit.com/linode and get a $20 credit to try out their fast and reliable Linux virtual servers for running your awesome app.
  • Visit the site to subscribe to the show, sign up for the newsletter, read the show notes, and get in touch.
  • To help other people find the show please leave a review on iTunes, or Google Play Music, tell your friends and co-workers, and share it on social media.
  • Your host as usual is Tobias Macey and today I’m interviewing Glyph about Automat, a library that provides self-service finite-state machines for the programmer on the go.

Interview

  • Introductions
  • How did you get introduced to Python?
  • What is a state machine and when might you want to use one?
  • There are a number of libraries available on PyPI that facilitate the creation of state machines. Why did you feel the need to build a new option and how does it differ from what was already available?
  • Why do you think developers fall into the trap of complicated conditional structures rather than reaching for a state machine?
  • For someone who wants to integrate Automat into their project how would they go about that and what are some of the gotchas that they should keep in mind?
  • What do the internals of Automat look like and how did you approach the overall design of the project?
  • What are some of the more difficult aspects of designing and implementing state machines properly?
  • What are some of the technical hurdles that you have been faced with in the process of building a library for implementing state machines?
  • What do you have planned for the future of Automat?
  • What are some of the most interesting use cases of Automat that you have seen?

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The intro and outro music is from Requiem for a Fish The Freak Fandango Orchestra / CC BY-SA