Code organisation

Hello,

i'm building my first site with this great framework and language that are Django and Python.

I try as much as possible to favor code reuse.

On one of my model, I do some work with the instance before saving it.

Works is mostly image related: resizing image, compressing, saving thumbs, and a couple more stuff.

I will need this behavior in almost all the projects that I will building, and even some other apps in the same project will need this feature: the blog, the comments, the directory…..

In this case, where to put this code ? What do guys and gals do usually in this situation ? 

Do you just put it in a custom (non app) folder like 'my_utilities' ?

Advices welcome.

Thanks,

Benj