[freiheit]

They generally do much better than a README: machine-parseable is the way to go.

Perl (CPAN) packages include a YAML file that specifies what other modules (packages) and what minimum version of each is required to configure, build and run the package. There's an ecosystem of tools available for turning a Perl package into an RPM or deb, some of which can even work recursively. Even before the YAML was standard in CPAN packages, it just wasn't that hard to parse out all the "use" and "require" statements to automatically detect all the required packages (and minimum versions of those). There's also a unit testing framework to make sure you don't accidentally introduce any incompatibilities with untested newer versions of required packages.

I haven't dealt with Ruby quite as much, but the gem format also includes dependency information and there's gem2rpm for RPM and dpkg-gem for deb packages.

I think I've only ever once had to build an RPM or deb package of a Python package, but Python seems to natively support building both formats; just call the same "build and install" method you'd usually use with an extra argument and you get a native package, which will use dependency information if the python package provided it.