    def get_task_proportions(self, data_loaders: Mapping[str, DataLoader]) -> Dict[str, float]:
        """
        Given a dictionary of `DataLoaders` for each dataset, returns what percentage of the
        instances for the current epoch of training should come from each dataset.  The input
        dictionary could be used to determine how many datasets there are (e.g., for uniform
        sampling) or how big each dataset is (e.g., for sampling based on size), or it could be
        ignored entirely.
        """
        raise NotImplementedError
Given a dictionary of `DataLoaders` for each dataset, returns what percentage of the
instances for the current epoch of training should come from each dataset.  The input
dictionary could be used to determine how many datasets there are (e.g., for uniform
sampling) or how big each dataset is (e.g., for sampling based on size), or it could be
ignored entirely.
allennlp/data/data_loaders/multitask_epoch_sampler.py