Tutorial 0 - Hello, world!

In this tutorial, you’ll take a really simple “Hello, world!” program written in Python, convert it into a classfile, and run it on the Java Virtual Machine.


This tutorial assumes you’ve read and followed the instructions in Installation. If you’ve done this, you should have:

  • Java 7 (or higher) installed and available on your path,
  • An env directory for your virtualenv
  • A tutorial directory with a VOC checkout,
  • An activated Python 3.4+ virtual environment,
  • VOC installed in that virtual environment,
  • A compiled VOC support library.

Start a new project

Let’s start by creating a tutorial0 directory in the tutorial directory alongside the voc directory you just cloned into:

$ mkdir tutorial0
$ cd tutorial0

So that your directory structure looks like:

├── env
├── ouroboros
├── tutorial0
└── voc

Then create a file called example.py in this tutorial0 directory. Add the following Python code to example.py:

print("Hello World!")

Save the file. Run VOC over this file, compiling the Python code into a Java class file:

$ voc -v example.py

This runs the VOC compiler over the example.py source file. The -v flag asks VOC to use verbose output so you can see what is going on. You will see output like the following:

Compiling example.py ...
Writing python/example.class ...

This will produce an example.class in the python namespace. This classfile can run on any Java 6 (or higher) VM. To run the project, type:

  • On Linux / OS X
$ java -classpath ../voc/dist/python-java-support.jar:. python.example
Hello World!
  • On Windows
> java -classpath ../voc/dist/python-java-support.jar;. python.example
Hello World!

Congratulations! You’ve just run your first Python program under Java using VOC! Now you’re ready to get a little more adventurous.