def get_default_python(python_runtimes):
    """
    Get the default python for the current build:
    - default to 2 if python_runtimes includes 2 (so that builds with 2 and 3 default to 2)
    - default to 3 otherwise.
    """
    return "2" if '2' in python_runtimes.split(',') else "3"