old_contents: import time
  from osbrain import run_agent
  from osbrain import run_nameserver
  
  
  def log_a(agent, message):
      agent.log_info('Log a: %s' % message)
  
  
  def log_b(agent, message):
      agent.log_info('Log b: %s' % message)
  
  
  def send_messages(agent):
      agent.send('main', 'Apple', topic='a')
      agent.send('main', 'Banana', topic='b')
  
  
  if __name__ == '__main__':
  
      # System deployment
      ns = run_nameserver()
      alice = run_agent('Alice')
      bob = run_agent('Bob')
  
      # System configuration
      addr = alice.bind('PUB', alias='main')
      alice.each(0.5, send_messages)
      bob.connect(addr, alias='listener', handler={'a': log_a})
  
      time.sleep(2)
  
      bob.unsubscribe('listener', 'a')
      bob.subscribe('listener', handlers={'b': log_b})
  
      time.sleep(2)
  
      ns.shutdown()
  
new_contents: import time
  from osbrain import run_agent
  from osbrain import run_nameserver
  
  
  def log_a(agent, message):
      agent.log_info('Log a: %s' % message)
  
  
  def log_b(agent, message):
      agent.log_info('Log b: %s' % message)
  
  
  def send_messages(agent):
      agent.send('main', 'Apple', topic='a')
      agent.send('main', 'Banana', topic='b')
  
  
  if __name__ == '__main__':
  
      # System deployment
      ns = run_nameserver()
      alice = run_agent('Alice')
      bob = run_agent('Bob')
  
      # System configuration
      addr = alice.bind('PUB', alias='main')
      alice.each(0.5, send_messages)
      bob.connect(addr, alias='listener', handler={'a': log_a})
  
      time.sleep(2)
  
      bob.unsubscribe('listener', 'a')
      bob.subscribe('listener', handler={'b': log_b})
  
      time.sleep(2)
  
      ns.shutdown()
  
subject: Fix example with wrong `handler` parameter name