keras/src/metrics/regression_metrics.py/MeanAbsolutePercentageError/__init__
class MeanAbsolutePercentageError:    def __init__(self, name="mean_absolute_percentage_error", dtype=None):
        super().__init__(mean_absolute_percentage_error, name, dtype=dtype)
        # Metric should be minimized during optimization.
        self._direction = "down"