Python has the [Zen of Python] as a guiding philosophy. I think IDL would have something a bit more practical. This is my take on IDL's philosophy:
>The Tao of IDL
>Interactive is better than compiled.
>Fast to write is better than fast to execute.
>But vectorized is better than loops;
>`WHERE` is better than `FOR`/`IF`.
>There are more uses of histograms than first meet the eye.
>A picture is worth at least ten thousand bytes of data,
>A million if its 3D and you can rotate it interactively.
>Whether direct or function, graphics are easy to create
>But the possibilities are endless.
>Backwards compatibility is great!
>But it doesn't mean you should index arrays with parentheses forever.
>IDL might not have started with objects,
>But it has them now, so use them!
>There are many file formats and each is the most important to someone.
>If you can't read the data, you can't analyze it.
>Keywords are a great idea -- especially
>If your parameter has a useful default
>Or is an optional output.
By the way, the [Bad habits] posting is very funny and relevant to Fortran/IDL users.
[Zen of Python]: http://www.python.org/dev/peps/pep-0020/
[Bad habits]: http://www.python.org/doc/humor/#bad-habits