code: def _get_dependency_definition(task_id, dependencies):
      
      set_upstream_statements = ''
      for dependency in dependencies:
        set_upstream_statements = set_upstream_statements + \
            '{0}.set_upstream({1})'.format(task_id, dependency) + '\n'
      return set_upstream_statements
docs: Internal helper collects all the dependencies of the task, and returns
        the Airflow equivalent python sytax for specifying them.