README.Debian in /usr/share/doc/PACKAGE-NAME usually has this information. Of course, some package maintainers aren't as nice as others in this regard. The pr

README.Debian in /usr/share/doc/PACKAGE-NAME usually has this information. Of course, some package maintainers aren't as nice as others in this regard. The problem is much simpler with Ruby packages since they have only one interface. Debian packages have many interfaces, and so it can never be as easy as that. I'll note that Debian/Ubuntu python packages work just as you expect: apt-get install python-twisted, then import twisted in your code.