NEUTRAL = 0
INFECTED = 1

class ControlModelM2(BaseBehaviour):
  NEUTRAL = 0
  INFECTED = 1
  def step(self, now):
    if self.state['id'] == NEUTRAL:
      self.neutral_behaviour()
    elif self.state['id'] == INFECTED:
      self.infected_behaviour()
    …
  def infected_behaviour(self):
    neutral_neighbors = self.get_neighboring_agents(state_id=INFECTED)
    for neighbor in neutral_neighbors:
      if random.random() < self.prob_infect:
        neighbor.state['id'] = INFECTED