Sean's Technology and Writing Blog

Mission Python: Errata and Updates

21 January 2019

My book Mission Python went through extensive quality controls before publication, with each listing built and tested by both myself and the tech editor. My own testing was carried out on both the Raspberry Pi and the Windows PC. I have played the game to completion many times, in addition to testing each listing as the game was built for the book.

However, I have been alerted to a few minor inaccuracies in the book, mainly in the instructions for running the code. There were also some tiny mistakes in the code (but nothing that stopped the game working).

I use this blog post to maintain a list of any errors and updates. We are incorporating these into the book when it is reprinted. If you got your copy recently, you may not have these issues.

My recommendation for installing Python and Pygame Zero is now to use the Mu Editor, which includes Pygame Zero and is available for Windows and macOS. On Raspberry Pi, use Thonny, which also supports Pygame Zero by default. Thonny is installed when you use Raspberry Pi OS with recommended applications. Using Mu or Thonny solves any challenges around installing Pygame Zero, while ensuring you have a version of Python that is compatible. When you run Mu, click Mode to check it’s on Pygame Zero mode. Enter your program in the big window, and then click the Play button to run it.
The instructions for running Listing 4-1 say that you can run it from IDLE. This will generate an error saying that the name 'images' is not defined. To run this listing, you need to run it from the command line using pgzrun listing4-1.py. For instructions on using the command line to run Pygame Zero programs, please see the Running the Game section in the book's Introduction. When you run this program, the game window will be blank because the program sets up the data but doesn't display anything on the screen yet. If you don't see any error messages and you do see a blank window, your program is working fine. (When you reach Listing 4-3, you should start to see the room on the screen in the window.)
The points made above also apply to Listing 4-2: you should run it using pgzrun listing4-2.py and not IDLE. The game window will be blank. You can't use the shell to test the program, but you can add instructions to the end of the program and then run it from the command line. You will see the output in the command line window. Below is some example code to add to the end of Listing 4-2 to complete Training Mission #1 in Chapter 4. Add this code right at the end of the listing, without any indentation. When you've finished testing, make sure you delete this test code to avoid any problems later on. ## Test code ## current_room = 45 generate_map() print(room_map)
On p118, in Listing 7-5, add the instruction generate_map() as shown below. If you need to make this change, you don't need to use Listing 8-3 in the book, which adds this instruction later. In later listings, the generate_map() instruction should come before the clock.schedule_interval() instruction where shown. ############### ## START ## ############### generate_map() clock.schedule_interval(game_loop, 0.03)
In Listing 8-2, the PLAYER_SHADOW dictionary uses animation frame 3 twice. The final image in the left dictionary should be images.spacesuit_left_4_shadow, for example, instead of images.spacesuit_left_3_shadow again. The same applies to the right, up, and down animation sequences.
On p164 in Listing 9-8, you can make the inventory easier to use by adding a delay to stop it cycling through the items too fast. After the display_inventory() instruction, add a time.sleep(0.2) instruction. This should be indented to the same depth as the display_inventory() instruction.
On p178, when you add the code from Listing 10-6 to Listing 10-5, you should save the program as listing10-6.py and run it with pgzrun listing10-6.py. The process and program still works if you reuse the listing10-5.py filename again as described in the book, but the correct process is to use listing10-6.py.
You can run Pygame Zero programs directly from IDLE by adding two lines to the code. As the first line, add:
import pgzrun
As the final line, add:
pgzrun.go()
There are two recipes in the code that are not required. They are hangovers from an earlier version of the game in which you began the game outside the spacesuit and had to repair it before you could wear it. The two recipes are [88, 58, 89] and [89, 60, 90]. This doesn't affect how the game plays: because objects 88 and 89 are not in the game, you can't use the recipe. If you were to add objects 88 and 89 when customising the game, and players were to try using them together with objects 58 and 60 respectively, you would see unexpected results.
If you're having difficulties getting the code running, I recommend you download and test my version of the code to see whether the problem still exists. If not, look for differences between your code and mine. In particular, indentation can be hard to spot and makes a difference to how the code works. If you can't get my code working, I recommend you try using Mu Editor on macOS or Windows, because it installs Pygame Zero for you and problems sometimes arise installing it in other ways. On the Raspberry Pi desktop, Pygame Zero is installed for you and you can use the Thonny Python editor.

If you experience difficulties, please see also my blog post about compatibility with different software and hardware platforms to those officially supported by Mission Python.

Many thanks to Adriaan van Niekerk, Stéphanie Noardo, Richard Park, Tim Byers, Ryan McLeod, Matt Schottel, Chris Myrick, and Barry Groden for telling me about these issues.

If you encounter other problems, please feel free to get in touch. We are incorporating these updates and corrections into the ebook and reprints of the paper book.

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