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