pkgsrc lists these features of pip, emphasis added:
- All packages are downloaded before installation. Partially-completed installation doesn’t occur as a result.
- Care is taken to present useful output on the console.
- The reasons for actions are kept track of. For instance, if a package is being installed, pip keeps track of why that package was required.
- Error messages should be useful.
- The code is relatively concise and cohesive, making it easier to use programmatically.
- Packages don’t have to be installed as egg archives, they can be installed flat (while keeping the egg metadata).
- Native support for other version control systems (Git, Mercurial and Bazaar)
- Uninstallation of packages.
- Simple to define fixed sets of requirements and reliably reproduce a set of packages.
I’d say the emphasised lines would be useful for any tool, not least a package manager.