Posts by Al.

Decimal, Binary, and Hexadecimal Odometers

It can be difficult to see how other number systems (such as binary and hexadecimal) work since they have a different amount of numerals than the ten numerals of decimal. But imagine that you are counting in these number systems using an old-fashioned analog odometer that has a different amount of numerals for each digit.

The following three odometers always show the same number, but they are written out differently in different number systems:
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Source Code Makeover: Demon Kingdom, Part 2

This is a continuation of Part 1. I make a lot of the same changes as before, mostly removing duplicate code.
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Source Code Makeover: Demon Kingdom, Part 1

In this blog post, I’m taking a game off of Pygame.org and going through it to make it more readable and extend its functionality. This is an intermediate level tutorial and assumes some familiarity with Python. This can be pretty helpful if you know programming basics but want to know, “How can I write better code?” (And because someone always brings it up, I have this disclaimer: Of course, these changes are my own subjective idea of “better” and not necessarily changes that another developer would make.)

Demon Kingdom by Logi540 is a defense game where monsters walk from the left side of the screen. The player needs to attack them by clicking on them, and can pick up gems to use for spells. If any monster reaches the right side of the screen, the player loses. Download source code.

The main theme of my changes is:

  • Removing duplicate code. Duplicate code is bad because if you have to change it (to add features or fix bugs) you may forget to change it in every duplicated place.
  • Remove magic numbers. Magic numbers are hard-coded integer values which are bad because they don’t describe what they represent. A better alternative is to use a constant instead (these are the ALL-CAPS variables).
  • Put sequential variables in lists and use loops. Instead of having variables named like spam1, spam2, spam3, and so on, it’s better to have a single list variable, and have a loop run code on each item in the list. This usually leads to a decrease in duplicate code.
  • Get rid of unneeded variables. Removing code reaps tons of benefits: there’s less code a programmer has to read and understand, less code that a programmer has to look through when debugging, and less code (usually) means less bugs and “moving parts” that could break.

Here’s the inital check in of all the files. The file I’ll be modifying is named demonkingdom_makeover.py. This program requires Pygame to be installed to run. I recommend downloading the game, playing it a couple times, and looking through the source code before continuing with this article. For each section, open up the diff link to see what the exact changes I made were.

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Comments on John Resig’s “Programming Book Profits” (and on Self-Publishing)

John Resig is the talented creator of the jQuery JavaScript Library and the author of the excellent book Pro JavaScript Technique. In January of 2008, he wrote a blog post entitled Programming Book Profits where he lists several things he wish he knew when starting out writing a programming book.

I wanted to repeat some of the things he said in that post with my own commentary, coming from the perspective of someone who has self-published technical books rather than going through a traditional publisher. I’ve used CreateSpace.com to publish all three of my books, and I haven’t had any problems with them. A special thanks to John for giving me permission to use his article here.

A summary of my points:

  • Publishers don’t do all that much to promote your book, and don’t offer an advantage over self-publishing here.
  • Writing interesting blog posts is a much more effective way to get publicity than buying advertising.
  • Christmas will effortlessly triple your sales, but have your book out there well before the holidays.
  • I use CreateSpace.com as my self-publisher, and haven’t had problems with them. The books only sell through Amazon, and directing readers from my book’s site to the Amazon page using the Amazon affiliate program gets a little extra cash per sale.

When you negotiate a contract with a publisher, and you receive an advance, that’s an advance of your future profits. I had no idea why I never realized this until after I received my first statement and saw -$3000 listed as my payout. It makes a lot of sense, in retrospect – but it was just a silly thing that never quite clicked with me.

Advances are usually pretty low (I think Apress’ typical one was $5000 for a first-time author). In talking with authors at other publishers you can usually expect something in that range – maybe slightly higher.

One thing about self-publishing is that there is absolutely no advance. 100% of the work needs to be done upfront before you see a dime. I wrote my books as a side project while I kept my day job. I don’t currently have any plans to drop my job to write full time.

No one buys eBooks. You’d have to be pretty… special… in order to not be able to find a free ebook of Pro JavaScript Techniques.

I’ve made my books freely downloadable under a Creative Commons license, which I credit entirely with the commercial success of the books. Had I simply made them available for purchase on Amazon, I don’t think anybody would have taken a chance with them. Piracy of the books by readers is not a concern for me, so much as piracy of other people selling my books (I’ve sent one copyright infringement notice to Amazon when someone posted the rough draft of “Hacking Secret Ciphers” for sale as an ebook.)

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Text Adventure vs. MUD vs. Roguelike vs. Dwarf Fortress

A text-style game is a common project for beginner programmers. These can be fun to do, but also require spending time up-front to design it is worthwhile. Before you start designing your own game, look at the design decisions of a few different text-style game genres.

Text Adventures

Also known as interactive fiction or IF, a text adventure game were the first incarnations of these types of games. They are single-player, turn-based (the game paused while the player typed in commands), and presented the user with an English text description of each room the player was in. The player was often a single character with an inventory of items picked up in the rooms. Commands were simple English phrases like "open door" or "get lamp".

West of House
You are standing in an open field west
of a white house, with a boarded front
door.
There is a small mailbox here.
> open mailbox

While the player could die, often the player did not have stats such as hit points, money, or experience points. Text adventures are puzzle-based (such as finding different rooms or figuring out which items to use where), rather than based on progressing in stats or levels.

Text adventure games are more than just “Choose Your Own Adventure” programs, because they take place in open sandbox worlds that the player can freely explore.

These are the simplest types of games to make. In fact, you don’t even need a real programming language to make one of these games. There is software specifically for creating text adventure games.

The 1993 hit Myst is an example of a graphical version of this genre. These games became more sophisticated with the graphic adventure game genre (or “point-and-click adventure games”), the most notable coming from LucasArts. Specialized software for making graphic adventure games also exists, chief of which is Adventure Game Studio.

  • Single-player
  • Turn-based
  • Player directly controls a single character
  • English text descriptions (not ASCII art)
  • English phrases for commands
  • Inventory
  • No stats or levels
  • Puzzle-based and role-playing story elements

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New Forums for the Books

I’ve been meaning to add forums to the website where readers of the programming books could talk to each other and ask questions. I’ve held off on doing this for a while until I could figure out a way to handle spam. However, I’ve decided instead to set up a subreddit for all three books (in effect, making Reddit the host for the forums).

Feel free to email me any questions you have as always, but these forums are also now available to use:

/r/inventwithpython

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