By transitive dependencies I mean that it will intall C when installing package A if A depends on B and B depends on C. It looks like it would do that.

As for 'obsoletes' I meant the case (this is from the RPM 'world') where on package changes names or 2 packages are combined into one, so let's say you maintain package A. Then you change its name to B because Oracle's lawyers have threatened to break your knees over a trademark ;-). Now everyone in the world depends on A so you declare that B obsoletes A so not their package will still install and corectly pull in your new package B. The same would happen if say you got together with another project and merged their project into yours. So you would 'obsolete' their old package name. Yeah, this probably doesn't apply to pip as much as RPM, it is more of feature of the package index server rather than pip itself perhaps.