Description of the problem / feature request:

When working with Java, it's possible to rely on third party jars using the java_import rule. The same should be possible for python. Following the same naming conventions as bazel already has, this might be called py_import.

The Python world uses eggs and wheels as the common formats for packaging dependencies, and both of these should be supported.

Feature requests: what underlying problem are you trying to solve with this feature?

I want to build python code using third party dependencies.

What's the output of bazel info release?

release 0.22.0

Have you found anything relevant by searching the web?

There is a [whl_import](https://github.com/bazelbuild/rules_python/blob/master/docs/python/whl.md) but this creates a new repository, where it's very easy to have name clashes (and it looks ugly, and obscures where on the disk the dependencies are kept)