RWT (Run With This) provides on-demand dependency resolution.

- Allows declaration of dependencies at runtime.  - Downloads missing
  dependencies and makes their packages available for import.
- Installs packages to a special staging location such that they're not
  installed after the process exits.
- Relies on pip to cache downloads of such packages for reuse.
- Supersedes installed packages when required.
- Relies on packages already satisfied.
- Re-uses the pip tool chain for package installation and pkg_resources for
  working set management.

WWW: https://pypi.python.org/pypi/rwt
WWW: https://github.com/jaraco/rwt