To install new packages:

1) Add your package to deps/requirements.txt. You should specify the version number
   using the "foo == x.y.z" notation so future upgrades can be done automatically.
2) Run deps/download_requirements, it will download the package to the deps dir.
3) Run the "impala-python" command, this should detect that requirements.txt changed and
   automatically rebuild the virtualenv.
4) Now in the python prompt, you should be able to import the new module.

To upgrade a package:

1) Edit deps/requirement.txt to use the version you need.
2) Go to step 2 above.