code: def Get(self, fields=None):
      
      if not self._field_defs and fields:
        raise ValueError("Metric was registered without fields, "
                         "but following fields were provided: %s." % (fields,))
  
      if self._field_defs and not fields:
        raise ValueError("Metric was registered with fields (%s), "
                         "but no fields were provided." % self._field_defs)
  
      if self._field_defs and fields and len(self._field_defs) != len(fields):
        raise ValueError(
            "Metric was registered with %d fields (%s), but "
            "%d fields were provided (%s)." % (len(
                self._field_defs), self._field_defs, len(fields), fields))
  
      metric_value = self._metric_values.get(_FieldsToKey(fields))
      return self._DefaultValue() if metric_value is None else metric_value
docs: Gets the metric value corresponding to the given field values.