code: def _get_workflow_by_uuid(workflow_uuid):
      
      from reana_db.models import Workflow
      workflow = Workflow.query.filter(Workflow.id_ ==
                                       workflow_uuid).first()
      if not workflow:
          raise ValueError(
              'REANA_WORKON is set to {0}, but '
              'that workflow does not exist. '
              'Please set your REANA_WORKON environment '
              'variable appropriately.'.
              format(workflow_uuid))
      return workflow
docs: Get Workflow with UUIDv4.
  
      :param workflow_uuid: UUIDv4 of a Workflow.
      :type workflow_uuid: String representing a valid UUIDv4.
  
      :rtype: reana-db.models.Workflow