code: def list_users(self, user=None):
      '''list users, each having a model in the database. A headless experiment
         will use protected tokens, and interactive will be based on auto-
         incremented ids.
      ''' 
      from expfactory.database.models import Participant
      participants = Participant.query.all()
      users = []
      for user in participants:
          users.append(self.print_user(user))
      return userf list_users(self, user=None):
      '''list users, each having a model in the database. A headless experiment
         will use protected tokens, and interactive will be based on auto-
         incremented ids.
      ''' 
      from expfactory.database.models import Participant
      participants = Participant.query.all()
      users = []
      for user in participants:
          users.append(self.print_user(user))
      return users
docs: list users, each having a model in the database. A headless experiment
         will use protected tokens, and interactive will be based on auto-
         incremented ids.