I have an application, written in Python, which is used by a fairly technical audience (scientists).

I'm looking for a good way to make the application extensible by the users, i.e. a scripting/plugin architecture.

I am looking for something extremely lightweight. Most scripts, or plugins, are not going to be developed and distributed by a third-party and installed, but are going to be something whipped up by a user in a few minutes to automate a repeating task, add support for a file format, etc. So plugins should have the absolute minimum boilerplate code, and require no 'installation' other than copying to a folder (so something like setuptools entry points, or the Zope plugin architecture seems like too much.)

Are there any systems like this already out there, or any projects that implement a similar scheme that I should look at for ideas / inspiration?