I am using bazel 0.27 and running these on an OSX.
Every directory is a self-contained example.
cd py_binary
bazel run -c opt foo:hello_world # builds and runs a python binary of hello_world.py.
You need docker to run the below command. (It is not working without a flag at the moment.)
cd py3_image
bazel run -c opt foo:hello_world --incompatible_use_python_toolchains=false # builds and runs a docker image of hello_world.py.