code: def register(self, category):
          
          def decorator(func):
              name = func.__name__
              key = f'{category}.{name}'
              self._metrics[key] = func
              return func
          return decorator
docs: Usage:
              @metrics.register('finance')
              def approved_funds(pronac, data):
                  return metric_from_data_and_pronac_number(data, pronac)