We have a Django application, and because of various aspects of Django (such as Django handling much of the heavy lifting), I expect that it's our most Python 3 ready chunk of code. Since I was working on it today anyways, I took a brief run at seeing if it would at least print help messages if I ran it under Python 3. As it turns out, making the attempt shows me that I need to cultivate some new coding habits in order to routinely write code that will be ready for Python 3.

What I stumbled over today is that I still like to write except clauses in the old way:

try:
   ....
except SomeErr, err:
   ....

The new way to write except clauses is the less ambiguous 'except SomeErr as err:'. Python 3 only supports the new style.

Despite writing at least some of the code in our Django application relatively recently, I still wrote it using the old style for except. Of course this means I need to change it all. I'm pretty certain that writing except clauses this way is not something that I think about; it's just a habit of how I write Python, developed from years of writing Python before 'except CLS as ERR' existed or at least was usable by me.

What I take away from this is that I'm going to need to make new Python coding habits, or more exactly go through the more difficult exercise of overwriting old habits with new ones. I'm sure to be irrationally annoyed at some of the necessary changes, especially turning 'print' statements into function calls.

(If I was serious about this, what I should do is force myself to write only in Python 3 for a while. Unfortunately that's not very likely.)

The good news is that I checked some code I wrote recently, and I seem to have deliberately used the new style except clauses in it. Now if I can remember to keep doing that, I might be in okay shape.

(Having thought about it, what would be handy is a Python linter that complains about such unnecessary Python 3 incompatibilities. Then I'd at least have a chance of catching my issues here right away.)

PS: Modernizing an old code base is a related issue, of course. I need to modernize both code and habits to be ready for Python 3 in both current and future code.

Sidebar: The timing and rationality of using old-style except

New style except was introduced in Python 2.6, which dates back to 2008. However, the new version of Python didn't propagate into things like Linux distributions immediately; it took two years to get it into an Ubuntu LTS release, for example (in 10.04). Looking back at various records, it seems that the initial version of our Django application was deployed on an Ubuntu 8.04 machine that would have had only Python 2.5. In fact I may have written the first version of all of the substantial code in the application while we were still using 8.04 as the host machine and so new-style except would have been unavailable to us.

This is of course no longer the case. Although not everything we run today has Python 2.7 available (cf), it all has at least Python 2.6. So I should be writing all my code with new style except clauses and probably some other modernizations.