Are there any languages which have an hierarchical repository which is structured so that one can easily browse and find what one needs? Or, arriving where it ought to be, discover that it does not yet exist?
CTAN seems pretty close, but is tightly focused on TeX, and CPAN is for Perl, not Python.
Hackage has a categories system which can be used to browse through all Haskell packages [0]. Unfortunately the categories are unstandardised, so it’s less useful than it could be — though the Flora project exists, which has improved the UI by standardising categories a bit [1].
CTAN seems pretty close, but is tightly focused on TeX, and CPAN is for Perl, not Python.