import abc
from collections import OrderedDict


LossStatistics = OrderedDict

class LossFunction(object, metaclass=abc.ABCMeta):
    @abc.abstractmethod
    def compute_loss(self, batch, skip_statistics=False, **kwargs):
        """Returns loss and statistics given a batch of data.
        batch : Data to compute loss of
        skip_statistics: Whether statistics should be calculated. If True, then
            an empty dict is returned for the statistics.
        Returns: (loss, stats) tuple.
        """
        pass
