Is it ever polite to put code in a python configuration file?

Question

One of my favorite features about python is that you can write configuration files in python that are very simple to read and understand. If you put a few boundaries on yourself, you can be pretty confident that non-pythonistas will know exactly what you mean and will be perfectly capable of reconfiguring your program.

My question is, what exactly are those boundaries? My own personal heuristic was

1. Avoid flow control. No functions, loops, or conditionals. Those wouldn't be in a text config file and people aren't expecting to have understand them. In general, it probably shouldn't matter the order in which your statements execute.
2. Stick to literal assignments. Methods and functions called on objects are harder to think through. Anything implicit is going to be a mess. If there's something complicated that has to happen with your parameters, change how they're interpreted.
3. Language keywords and error handling are right out.

I guess I ask this because I came across a situation with my Django config file where it seems to be useful to break these rules. I happen to like it, but I feel a little guilty. Basically, my project is deployed through svn checkouts to a couple different servers that won't all be configured the same (some will share a database, some won't, for example). So, I throw a hook at the end:

try:
    from settings_overrides import *
    LOCALIZED = True
except ImportError:
    LOCALIZED = False

where settings_overrides is on the python path but outside the working copy. What do you think, either about this example, or about python config boundaries in general?

Answer 1

There is a Django wiki page, which addresses exactly the thing you're asking. http://code.djangoproject.com/wiki/SplitSettings

Do not reinvent the wheel. Use configparser and INI files. Python files are to easy to break by someone, who doesn't know Python.