How does bazel choose the python version?

Question

I'm running a python binary target with bazel run xxx and in the target I'm doing print(sys.version). This outputs Python version 3.6.8 (default, Jan 14 2019, 11:02:34)

When I type the python command directly, I get Python 3.7.3 (default, Apr 3 2019, 19:16:38)

Why/how did bazel choose a different python version?

Answer 1

Bazel will choose different python versions based on the configuration of the build. If nothing is overriden, bazel will use its default python version. This can be overridden by passing --python_version=<some_version> when running a bazel command.

https://docs.bazel.build/versions/master/be/python.html#py_binary.python_version https://github.com/bazelbuild/rules_python/blob/120590e2f2b66e5590bf4dc8ebef9c5338984775/python/BUILD#L43