def __init__(self, *datasets: Dataset, dict_transform: Optional[Callable] = None):
        """
        Args:
            datasets: params count of datasets to merge
            dict_transform: transforms common for all datasets.
                (for example normalize image, add blur, crop/resize/etc)
        """
        self.length = len(datasets[0])
        assert all(len(x) == self.length for x in datasets)
        self.datasets = datasets
        self.dict_transform = dict_transform

        Args:
            datasets: params count of datasets to merge
            dict_transform: transforms common for all datasets.
                (for example normalize image, add blur, crop/resize/etc)
        
catalyst/contrib/data/dataset.py