code: def pick(self, connections):
          
          if len(connections) == 1:
              return connections[0]
  
          def key(conn):
              return (datetime.min
                      if conn.backoff_time is None
                      else conn.backoff_time)
  
          return min(*connections, key=key)
docs: Picks a connection with the earliest backoff time.
  
             As a result, the first connection is picked
             for as long as it has no backoff time.
             Otherwise, the connections are tried in a round robin fashion.
  
          Args:
              connections (:obj:list): List of
                  :class:`~bigchaindb_driver.connection.Connection` instances.