code: def sub_map(self, counters_map):
      
      for counter_name in counters_map.counters:
        self.increment(counter_name, -counters_map.counters[counter_name])
docs: Subtracts all counters from the map.
  
      For each counter in the passed map, subtracts its value to the counter in
      this map.
  
      Args:
        counters_map: CounterMap instance to subtract.