def __init__(self, **kwargs):
        """
        Args:
            **kwargs: Keyword-arguments passed to ``super().__init__`` method.

        Raises:
            ValueError: if train argument is False (MnistMLDataset
                should be used only for training)
        """
        if "train" in kwargs:
            if kwargs["train"] is False:
                raise ValueError("MnistMLDataset can be used only for training stage.")
        else:
            kwargs["train"] = True
        super(MnistMLDataset, self).__init__(**kwargs)
        self._filter()

        Args:
            **kwargs: Keyword-arguments passed to ``super().__init__`` method.

        Raises:
            ValueError: if train argument is False (MnistMLDataset
                should be used only for training)
        
catalyst/contrib/datasets/mnist.py