keras/src/losses/losses.py/LossFunctionWrapper/__init__
class LossFunctionWrapper:    def __init__(
        self,
        fn,
        reduction="sum_over_batch_size",
        name=None,
        dtype=None,
        **kwargs,
    ):
        super().__init__(name=name, reduction=reduction, dtype=dtype)
        self.fn = fn
        self._fn_kwargs = kwargs