def add_metric(self, labels, value, timestamp=None):
self.samples.append(Sample(<EOL>self.name + '<STR_LIT>',<EOL>dict(dict(zip(self._labelnames, labels)), **value),<EOL><NUM_LIT:1>,<EOL>timestamp,<EOL>))<EOL>
Add a metric to the metric family.

        Args:
          labels: A list of label values
          value: A dict of labels