Python for Android

I installed SL4A (Scripting Layer for Android) and Python for Android on my new Android Phone last night, and I've got to say this makes my phone the neatest portable device I've had since my HP 200LX.

The 200LX was basically an IBM PC-XT that fit in your pocket. It was a clamshell that ran a ROM version of DOS that was even capable of running early versions of Windows if you really, really wanted. My interest was more in running full DOS IDE packages like Turbo Pascal, Modula-2, Turbo C/C++, FORTH, etc. It also had a spreadsheet (Lotus 1-2-3) on ROM, ran dBase and the Clipper compiler well, and a host of other things. I kept one with me for over 10 years, long past its day, because I couldn't find anything comparable that I could carry with me as well and do so much with. There's nothing like being able to whip out a machine with a decent compiler on it while your wife is in the fitting rooms at the mall.

Well now I've got Python on my Android phone. This was my second try.

A False Start
Initially, I did a search on the Play Store. There I found something called QTPython+ that was a free download with at least a couple of positive reviews. Well, I couldn't figure out what it was up to. Its programs don't use normal Python I/O, and so far as I could tell (following the in-app link to the dev website), it's not that well documented. I'm clearly missing something, but it didn't work out for me.

Then, while paging idly through a copy of Android Development with Eclipse, I saw a mention in a later chapter about Python and other scripting languages. I got my phone and went out to the SL4A site right away, book in one hand, Android phone in the other.

The SL4A Install
For those that haven't been through it yet, it's not difficult to do the install, but it's not what you'll be used to from Google Play, or the Amazon App Store, either. At the SL4A site, you'll download and install the latest version of SL4A, which more or less is the support layer for the scripting language. I downloaded sl4a_r6.apk, which would be the R6 version of it. By itself, it doesn't get you much. I think you can get a command line with it.

The next step is to get the Python installer from the Python for Android site. I pulled one marked for R6, Python_for_Android_R6.apk. This is Python 2.6.2, there's another package for Python 3.

Either way, when you install that and start it up you'll get a menu asking whether you want to "Install". This seems confusing (at least it did to me late last night) as you'll ask yourself "Isn't that what I just did?" Actually, you've installed the installer. Click install and wait a few moments while it goes out and gets the other packages you need for a working Python install.

After that, you'll start the app from the SL4A icon. There you'll see a list of the example Python modules the bundle comes with. There are some good examples of starter Android apps there. But you don't have to do things the "Android Way" if you don't wish...

Command Line Junkie
You can also edit your own command-line/text-console Python programs. My first go was an off-the-top-of-my-head version of Guess.py from Invent Your Own Computer Games with Python (the textbook I'm using to start students off with Python in class this year.)

It had to be modded a bit for Python 2, of course, but it worked like a charm.

What fun!

The Source Code (as if you care) ;)

from random import randint
num=randint(1,20)
print 'I am thinking of a number between 1 and 20.'
print 'Try to guess it in 6 guesses or less.'

guesses = 0
guess = 0

while guesses<6:
    print 'Your guess? ',
    guess = int(raw_input())
    guesses = guesses + 1

    if guessnum:
        print 'Too high.'

    if guess==num:
        break

if guess==num:
    print 'You got it in ',
    print guesses,
    print ' guesses!'

if guess!=num:
    print 'Too bad, the number was ',
    print num

Yet Another Look at Graphics and Sound on Python

Graphics

The more I look at it, the more I think the turtle module may be my answer for the graphics I need in the classroom. To recap, the basic ability I need from graphic in a classroom programming language is basic drawing and sprites. Cell or tile based graphics would be a big plus. In the non-python arena, Greenfoot pretty well has this covered for Java. It includes nice features like collision detection and distance determination as well.

Python's turtles can pretty well be treated as sprites. It's possible to have multiple simultaneous turtles in the current python versions. They can also be given unique appearances. It seems that the ability to use an image is there, but the documentation I've seen makes it look like a reserved feature. I'll have to look more into that.

Repurposing things like this always introduces an extra layer of complexity in the classroom. Students start to feel jerked around if you go and teach them that something is one thing, then start using it to do something else that doesn't follow from the first. In this case, perceiving the turtle as an indicator of where the drawing focus is when using turtle graphics, to forcing it into use as a free-moving entity that has various game behaviors we've associated with it.

It's not insurmountable, in this case, but it is more of a shift in thinking than a dedicated sprite class that aren't turtles by nature (perhaps a parent class of the turtle?)

In this case it's not a big deal, but in the classroom when little shifts like this start piling up one on another it gets harder to for the students to keep things straight and commit them to long term memory.

Another disadvantage of turtle graphics is that I pretty well have to develop my own material for class. I don't have a nice, pre-written book like Invent Your Own Computer Games with Python to draw on. That book is pretty much what let me bring python into my classroom. Using turtle graphics means that I have to write my own lessons using that module.

Sound

I still don't have a good answer for sound. The platform-independent library for sound in python has been taken out of the standard library. Sound is an important part of interacting with the computer for my students. When we've had teams developing video games using Greenfoot and Java in the past, it's not been unusual for the teams to have one of four students spend most of their time creating sounds and music for the games.

Python doesn't even have the ability to go "beep" without a platform-dependent library being added to the core package, as far as I can tell. That's pretty pathetic, what with it being so far to this side of 1983 and all. There are days when I wish the classroom was still filled with 8-bit computers. This is one of the reasons why.

So now, the ability to make sounds is the main thing missing from python so far as my use in class is concerned. I can still use Pygame for that, or have the students call platform-dependent system commands to produce sound.

Invent with Python Version Dependencies

I was able to take some time in class today to work on figuring out version dependencies in the programs in Invent Your Own Computer Games in Python. I started with the obvious in the early chapters, changes to print() and input() for Python 2.7.

Then I jumped forward to the chapters that use Pygame. I installed Pygame on the lab computer I was at, which was a Mac running Lion, and was pleased to have it function without having to install all the SDL libraries. Then I tried out the example programs from chapters 17-20 in Invent with Python.

All Clear
It turns out that these all worked fine, without any modification from the code in the book. Since they're mostly a smattering of python holding together a pygame program. ;)

That means I can go around to the lab computers, install Python 2.7 and Pygame, and have that ready for when the students get to the later chapters. I'll take a part of a class period to go over the differences between 3.x and 2.x, then set them loose.

Future Changes
Meanwhile, I'm going through the exercises in the earlier chapters. In the future, I'll start the class with Python 2.7 and have them use the programs with the minimum modifications necessary to work with 2.7. That way the material in the book will still be as close as possible to the example code.

I'll also be providing the students with a page on our class website linking to the specific versions of Python and Pygame we're using in class for the different possible platforms they have at home.

Started Python in Class Today

Today my middle school (7-8th grade) classes started Python with the Sweigart book. Everything went well for all students. Had to show one where to find '*' on the keyboard and another how to edit a file, but that's expected.

I have to write up some turtle graphics exercises before they get to the Pygame-based content, now.

I may try using Pygame with Python 2.7 on the Mac. I've been encouraged to do so, so if time permits, I'll try it myself then pick a student or two to be trailblazers for the rest.