Mixed version Python example
The question is how to support multiple version of Python in a single bazel project without resrting to wrapping one of the version as a generic shell script.
Initial setup would work for each target called separately with corresponding --python_top (or --python_path):
$ bazel build -s //example:old_test
$ bazel build -s //example:new_test --python_top //tools:python3
But that is less then optimal.