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Python on Android -- Easy as Pie

Here's what I did to get Python running on my HTC Incredible:

Step 1:  Install a barcode scanner, so that it's easier to install custom apps:  Install ZXing app

Step 2:  Install the SL4A application (Scripting Layer for Android) by going to the SL4A project home page and running the previously installed "Barcode Scanner" app (the title on the icon of the ZXing app) to scan the SL4A's barcode (or just click the link if you're reading this on your Android). This downloads a .apk file which you then run to install this app directly onto your phone, since it's not yet available in the Market. You might have to change your phone's settings to allow installing non-Market apps -- go to Settings / Applications and make sure "Unknown sources" is checked.

Step 3:  Install the Python interpreter:

1. Run app SL4A.
2. Press the menu button, then View, then Interpreters.  You should only have Shell at first.
3. Press the menu button, then Add, then select Python 2.6.2. After the .apk file for Python downloads, run it to install it.

Now you can edit and run Python scripts on your Android, and you have a lot of the Android functionality available. Here's my first test script:

import android

droid = android.Android()

droid.ttsSpeak('Hello World')

You can press Help to see the API that's available, it's a subset of the entire Android API.

Announcing New Consulting Offerings

We've actually been doing consulting for a while, and now we're formalizing it into two product areas:

• PyGuys - Python and open source based solution consulting
• PyCOE - Python Center of Excellence, we help you set up a process or organization inside your company to encourage adoption of Python

Summary of Python Web Frameworks, Beginning of 2008

Let me summarize our recommendations for Python web frameworks:

• Pylons: for database-driven applications
• Plone (built on Zope3): for CMS (content management systems)
• Twisted: for multiple/custom network protocols or extremely high volume

Overall, the Python web community is seeing a lot of active development and evolution in solutions. Whereas the Ruby community has one go-to web framework (Ruby on Rails), the Python community has a plethora of choices. Luckily, a Python standard was created, PEP 333 aka WSGI (pronounced "whiskey" but stands for Web Server Gateway Interface), which provides a standard component architecture for Python web servers. All of the above frameworks support this standard now. This interface standard allows plug-and-play middleware.

We recommend Pylons for database-driven application development because internally it is built on WSGI. If TurboGears 2.0 development proceeds as designed and it is written on top of Pylons, then we will recommend it. Here are the middleware components that we recommend using with Pylons, and the features of each that we really love:

Database ORM: SQLAlchemy

• well designed: provides nice object interface to SQL tables, but also let's you get to underlying SQL if you want to
• really efficient: can load entire graph of objects in one SQL query - e.g., load item and line item details in one round-trip to the database

Templating: Mako

• fast: it's the fastest of the Python templating engines
• simple: you use standard Python in your templates, instead of custom tag libraries

Request Dispatching: Routes

• flexible: regular expressions with intelligent name binding to map tidy-looking urls to your internal object hierarchy

Form handling: ToscaWidgets

• no repetition: you model your form elements using Python objects, and use this model both for display and validation
• flexible: you can either use the default or specify your own template for html generation

Every category of middleware above has competition, but these are our current recommendations. Even though Pylons is a relatively new project, it is built on more mature components that are on at least their second major version.

Why Python?

Here's a question I get sometimes: why did we use Python? I had been programming in J2EE/Java for six years before ProjectPipe. I had used most of the major technology areas in J2EE: ejb, servlet, jsp, jms, etc. I had lead several successful projects that mostly used BEA's WebLogic app server (for a while it was the best J2EE app server), though I also used the JBoss/Tomcat combination as well (mostly during development because it was faster to reboot).

We're not the only people who have left J2EE for hopefully greener pastures. Bruce Eckel just wrote
an article about people leaving Java for Ruby. I left Java for Python. I left for two reasons: 1) my buddy Mike bugged me to look into Python and 2) once I got over the white space/indentation Python issue, I found my productivity is higher. It's difficult to compare your productivity when using two different technologies, because once you solve a problem using one technology, you've learned some things and it's easier to solve the same problem in a different technology. Anyway, the only concrete difference I can offer is that it used to take about a minute to boot up a J2EE app server, but I can boot up my Python app server in 2 seconds. If you consider that during development you might reboot a hundred times in a day (you usually don't have to reboot in either technology if you just change a web page), then you can see that you might lose 6000 sec (100 x 60 sec) or 100 minutes using J2EE vs. 200 sec (100 x 2 sec) using Python. Of course, when your app server is rebooting you might look over code, but on the other hand it's very distracting to wait an entire minute before you can test changes you just made -- you're just as likely to keep surfing the web an extra ten minutes while waiting for your app server to finish booting up. And since J2EE is so damn complicated, it's tough to write unit tests -- I've done it occasionally in J2EE, but you usually have to either test outside of J2EE or go to the trouble of setting up and using the Cactus testing framework. If you write tests using Cactus, you're still stuck with your app server boot time.

The Python community has a number of database and web frameworks available, but Mike and I chose
Twisted for our networking and Nevow for our web framework. We rolled our own database support (written on top of Twisted). Mike was the instigator to use Twisted -- it took a while to convince stubborn me to use it, but after looking around, I grew comfortable because the guys developing it are really smart, and their arguments on the simplicity and scalability of their async approach sold me.

I would say that the only major thing I miss from Java is the boost in performance you get with Java's excellent JIT (Just In Time) compilers that come with the JVM. A while ago in an old weblog of mine,
I made some simple performance measurements and found that Java with JIT is something like an order of magnitude faster than Python. Though I'm keeping my eye out on the PyPy project which is working on JIT technologies for Python (which is especially difficult because of the dynamic nature of the language).