Hello, I've spent a few evenings working on a project to be able to write Android applications in Python by compiling Python source into Java source. I thought I'd share what I have in case there is interest in this (maybe even outside of Android development). I see this project having two parts, a Python to Java converter and a very basic simulated/stubbed out Java/Android API (so that one could write unit tests in python and run them in python, before compiling everything into Java).
Of course 100% Python to Java is not possible or practical to implement in a reasonable amount of time but I think enough could be implemented so that we could have 100% Python syntax with maybe 50% Python semantics and 50% Java semantics. I think just getting to that point would be a huge productivity gain on working with any java frameworks/APIs. Over time I think there can be work arounds for things that Java can't do like multiple inheritance, dynamic class creation, duck typing, etc. So, how does it work? I use Pythons ast and symtable modules to walk the source code and try to infer the possible types that a variable can have. This gives me the type information that Java will need. Then another pass generates Java source using this type information. There is nothing particularly magical especially since duck typing isn't implemented and you can't change the type of a variable after you've assigned to it the first time. So you have to be very careful with the Python code you write, think of it as statically typed Python where you don't have to declare types since they are inferred. I haven't gotten to lists and dictionaries yet but the principles will be the same, you can't have heterogeneous lists so the first thing you put in a list will provide that lists type. Why not use PyPy? It's possible to achieve some of my goals with PyPy and in some cases it will achieve a lot more than I will ever attempt to implement. One advantage of PyPy is that it supports a lot more of Pythons dynamism (for one, PyPy generates code from a loaded Python module while py2j uses static python source files). There are two major problems with PyPy for my purposes: 1) it generates specialized jvm byte code that the dalvik vm cannot convert 2) because PyPy is more pythonic it will be much harder to compile code in a way that will just plugin into the Android APIs, with PyPy you can't import Java packages or inherit from Java classes as you would have to do to write Android apps. Code I have so far is hosted here: https://bitbucket.org/eukreign/py2j/src I would say it's still more of a prototype than even alpha level code. You can see an example of input file and output in the samples directory. Also, the bottom of both analyze.py and compiler.py have a ton of unit tests you can look at to see what is possible so far. If you have questions or are interested in helping me please send me an email. - lex -- You received this message because you are subscribed to the Google Groups "Android Developers" group. To post to this group, send email to [email protected] To unsubscribe from this group, send email to [email protected] For more options, visit this group at http://groups.google.com/group/android-developers?hl=en
