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500 Lines or Less

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Number of watchers on Github 18263
Number of open issues 42
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Main language TeX
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Closed pull requests 5+
Last commit about 2 years ago
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Repo Last Updated 11 months ago
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500 Lines or Less

What I cannot create, I do not understand.

-- Richard Feynman

This is the source for the book 500 Lines or Less, the fourth in the Architecture of Open Source Applications series. As with other books in the series, all written material will be covered by the Creative Commons - Attribution license, and all code by the MIT License: please see the license description for details. In addition, all royalties from paid-for versions will all go to Amnesty International.

The production of this book has been made possible by the financial support of PagerDuty.

PagerDuty Logo


Every architect studies family homes, apartments, schools, and other common types of buildings during her training. Equally, every programmer ought to know how a compiler turns text into instructions, how a spreadsheet updates cells, and how a database efficiently persists data.

Previous books in the AOSA series have done this by describing the high-level architecture of several mature open-source projects. While the lessons learned from those stories are valuable, they are sometimes difficult to absorb for programmers who have not yet had to build anything at that scale.

500 Lines or Less focuses on the design decisions and tradeoffs that experienced programmers make when they are writing code:

  • Why divide the application into these particular modules with these particular interfaces?
  • Why use inheritance here and composition there?
  • How do we predict where our program might need to be extended, and how can we make that easy for other programmers?

Each chapter consists of a walkthrough of a program that solves a canonical problem in software engineering in at most 500 source lines of code. We hope that the material in this book will help readers understand the varied approaches that engineers take when solving problems in different domains, and will serve as a basis for projects that extend or modify the contributions here.


Name Affiliation Project Online GitHub
Mike DiBernardo Wave editorial MichaelDiBernardo
Amy Brown indie editorial amyrbrown
Allison Kaptur Dropbox byterun akaptur
Audrey Tang, Socialtext, Apple spreadsheet audreyt
Brandon Rhodes Dropbox contingent brandon-rhodes
Carl Friedrich Bolz King's College London object model cfbolz
Cate Huston   Image Filter app catehstn
Christian Muise University of Melbourne flow-shop haz
Daniel Jackson   same-origin-policy    
Daniel Rocco BrightLink Technology contingent drocco007
Dann Toliver Bento Box dagoba dxnn
Dessy Daskalov Nudge Rewards Pedometer dessy
Dethe Elza   blockcode   dethe
Dustin Mitchell Mozilla cluster   djmitche
Erick Dransch   Modeller EkkiD
Eunsuk Kang   same-origin-policy    
Greg Wilson   web-server gvwilson
Guido van Rossum Dropbox crawler gvanrossum
A. Jesse Jiryu Davis MongoDB crawler ajdavis
Jessica Hamrick University of California, Berkeley sampler jhamrick
Leah Hanson Google static analysis astrieanna
Leo Zovic   event-web-framework    
Malini Das Twitch ci malini
Marina Samuel Mozilla ocr emtwo
Ned Batchelder edX templating engine nedbat
Santiago Perez De Rosso   same-origin-policy    
Taavi Burns Previously at Points, now at PagerDuty data-store taavi
Yoav Rubin Microsoft In-memory functional database yoavrubin

Technical Reviewers

Amber Yust Andrew Gwozdziewycz Andrew Kuchling
Andrew Svetlov Andy Shen Anton Beloglazov
Ben Trofatter Borys Pierov Carise Fernandez
Charles Stanhope Chris Atlee Chris Seaton
Cyryl Potnicki-Chudyk Dan Langer Dan Shapiro
David Pokorny Eric Bouwers Frederic De Groef
Graham Lee Gregory Eric Sanderson James O'Beirne
Jan de Baat Jana Beck Jessica McKellar
Jo Van Eyck Joel Crocker Johan Thelin
Johannes Frmann John Morrissey Joseph Kaptur
Josh Crompton Joshua T. Corbin Kevin Huang
Maggie Zhou Marc Towler Marcin Milewski
Marco Lancini Mark Reid Matthias Bussonnier
Max Mautner Meggin Kearney Mike Aquino
Natalie Black Nick Presta Nikhil Almeida
Nolan Prescott Paul Martin Piotr Banaszkiewicz
Preston Holmes Pulkit Sethi Rail Aliiev
Ronen Narkis Rose Ames Sina Jahan
Stefan Turalski William Lachance
500lines open issues Ask a question     (View All Issues)
  • over 2 years Some error in project "ocr"
  • over 2 years DBDB > Organisational Units > Inserting and Updating, `` should be `` .
  • over 2 years scrapy
  • over 2 years crawler vs scrapy
  • over 2 years Modeller uses displaylists which are deprecated.
  • over 2 years Unmatched template tag in Templite class comment
  • almost 3 years Lisp code indentation at An Event-Driven Code Framework
  • almost 3 years MAking your own filters
  • almost 3 years Publish on
  • almost 3 years Incomplete citation in Dagoba article
  • about 3 years cluster one unit test may not passed
  • about 3 years An unreasonable infinite loops in ‘ci/code/’
  • over 3 years Crawler: How to fix the error "ConnectionRefusedError: [Errno 111] Connection refused"?
  • over 3 years What happens when a reponse takes very long
500lines open pull requests (View All Pulls)
  • Edits to the web server chapter.
  • Backporting typesetting changes into Dagoba copyedits
  • [catechism]move raise logic to matcher constructors
  • Copyedits on Same-Origin Policy in Alloy chapter
  • Event-driven web framework edits
  • Edits to the Contingent chapter
  • fix web-server attribute error
  • Fix error in 'web-server.markdown'
  • Removed the '' at the beginning of the sed command
  • small fix that replaces "Replica" with a link to the section
  • flake8 recommended changes
  • Crawler: fix a missing white space to separate 2 words
  • use an efficient and short method to get max value's index
  • modify error in the commentary
  • CI: Iterate through copy of dictionary that is modified during loop
  • fix parse_link in
  • erase 's'
  • Added Shapes and Colors to the 3D Modeler
  • Web-server: fix "'case_no_file' object is not callable"
  • Fixed to build a doc in python3
  • Crawler corrections January 2017
  • Crawler project: fix error caused by aiohttp update that use URL object replace url str
  • :bug: fix mixing URL and string in crawler
  • a typo
  • Fix syntax error
  • add requirements.txt
  • Convert to Python3
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