plugin development best practices

[Flavio]

Hi,

Nowadays the addition of functionality to programs by means  of
plugins is very frequent.

I want to know the opinions of experienced Python developers about the
best practices when it comes to developing a plugin system for a
Python package.

Should plugins be modules in a separate package?
Should there be a registry  of available plugins? how would such a
registry  be implemented? etc.

thanks,

Flávio