Cocoa, Python and the quest for platform independence

For the past few days, I’ve been looking into Apple’s Cocoa infrastructure in some detail. The reason once again stems from my research projects. All our code is in platform-independent Python meaning that we can develop on any of the 3 popular operating systems and then run on any others. This has been a great advantage since the three members of our team each run different OSes. For most of the time our project was purely command-line and text input based, using graphics only for the final display. However we have now come to the point where we need to fork our system into two different systems: one for architects and one for artists. How each program will develop is something that we will work on over the next few weeks, but one thing is clear: for the artists at least, a purely textual interface will simply not do.

Till now our system had been accepting an instruction file as input. While this method of using a instruction was very powerful (we could essentially embed our own programming language), this not the direction we want to go with the artists. And besides, not every artist wants to sit down and right pages of instruction to draw a picture, we might as well ask them to write the program themselves. It would be best to create a GUI for them to use. Even before this had been clear, I had written a simple interface that was essentially a text editor containing a hook to our Python backend. It was written in Tk, was exceptionally ugly, but got the job done.

My Tk Interface running under Leopard

Now I think the Tk toolkit is capable of letting me create the entire GUI interface that I have in mind and it will be cross platform as well, but there’s one problem: it’s ugly, especially on the Mac. I think this is because the Python Tkinter version doesn’t use Aqua (like Tcl/Tk), but rather uses X11. Though I spend a lot of my time in Vim and at the command line, I’m still a fan of good looking user interfaces (see my last post). As a result I would feel rather guilty about making something that I know would look bad on the platform it would be used most. So like a good programmer off I went to find a solution.

I thought I would be able to use Cocoa to create a front end, especially since Xcode now has support for the PyObjC bridge. Unfortunately this has turned out to be much harder than it at first appeared. Cocoa is Apple’s very powerful object oriented API. It is almost everything you will ever need to create a Mac application. While it allows to create native applications by leveraging the powerful infrastructure Apple provides you, it also doesn’t allow you to perform the sort of rapid duct-tape styling programming that Python and UNIX encourages. In Python it’s very easy to write your core application in Python with any number of GUI front-ends that are easily interchangeable. Cocoa, on the other hand, is not another GUI toolkit that you can simply add to the mix. If you want to use, you’ll have to invest a certain amount of time in learning your way around.

Python can’t communicate with Cocoa directly. To¬† have your Python programs leverage Cocoa, you need to go through the PyObjC bridge. Though the bridge is certainly effective and I could use it, I’ve been having troubles finding decent documentation. Apple’s own tutorial is the sort of document I’m looking for, but it is dangerously out of date. Lacking a proper tutorial, I would have to figure out a lot of things on my own. Once again, a large time investment.

Considering that I have only two weeks left to make real progress on my project and that learning Cocoa or Objective-C was not my original goal, I’ve decided not to pursue that avenue at the moment. I would certainly love to learn Cocoa at some point in the future and PyObjC seems like it could become a very powerful tool. But I simply don’t have the time at the moment. I am going to start working on a proper GUI interface in Tkinter. Perhaps sometime later this year, I’ll get back to some Cocoa.


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Shrutarshi Basu

Programmer, writer and engineer, currently working out of Cornell University in Ithaca, New York.

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