code: def tally(self, name, value):
          
          value = value or 0  # Protection against None.
          # Start at 0 if this is the first value.
          if 'used' not in self.usages[name]:
              self.usages[name]['used'] = 0
          # Increment our usage and update the "available" metric.
          self.usages[name]['used'] += int(value)  # Fail if can't coerce to int.
          self.update_available(name)
docs: Adds to the "used" metric for the given quota.