code: def get_category(self, metric):
          
          tags = ','.join('%s=%s' % (k, v) for k, v in
                          sorted(metric.metric_name.tags.items()))
          return '.'.join(x for x in
                          [self._prefix, metric.metric_name.group, tags] if x)
docs: Return a string category for the metric.
  
          The category is made up of this reporter's prefix and the
          metric's group and tags.
  
          Examples:
              prefix = 'foo', group = 'bar', tags = {'a': 1, 'b': 2}
              returns: 'foo.bar.a=1,b=2'
  
              prefix = 'foo', group = 'bar', tags = None
              returns: 'foo.bar'
  
              prefix = None, group = 'bar', tags = None
              returns: 'bar'