Description
pip_import currently installs all the wheels in a single repository, the same repository as the requirements.bzl file. That implies loading the requirements.bzl file in WORKSPACE also builds source packages for which wheels are not available (e.g. pysam). This makes the initial load slow, and requires all users to have the right environment setup to build any source packages into wheels, even if they don't do any python in their work.
It will be nice to have a "no-deps" mode where the requirements.txt file is expected to be the transitive closure (e.g. from pip freeze), and we have a separate repo for each package (relying on the --no-deps argument to pip wheel), such that they are downloaded and potentially built on demand, rather than on first load.
This also allows users to skip a dependency from pip altogether, and provide their own substitute by appending to the requirement dict.