Rules for external python packages in bazel.

See WORKSPACE for defining external libraries

See demo/third_party/BUILD for defining python libraries based on them

See demo/src/app.py for imports that hack sys.path for loading external libraries.

See demo/src/bundle_app.py for loading multiple external deps using a single rule.

Future plans:

• virtualenv_bin and virtualenv_test targets. Easy to use, depending only on pip
• Speak with bazel devs for md5 support in new_http_archive
• Speak with bazel devs for getting eggs into runfiles

Limitations:

• The build is reproductible but is not portable, as the loader libs wil work with local absolute paths.