def __init__(self, src):
        """
        Args:
            src (FloatTensor): a sequence of source words tensors
                    with optional feature tensors, of size (len x batch).
        """
        self.src = src
        self.previous_input = None
        self.previous_layer_inputs = None
        self.cache = None

        Args:
            src (FloatTensor): a sequence of source words tensors
                    with optional feature tensors, of size (len x batch).
        
dpkd/transformers/examples/research_projects/bertabs/modeling_bertabs.py