    def get_input_dim(self) -> int:
        """
        Returns the dimension of the vector input for each element in the sequence input
        to a `Seq2VecEncoder`. This is `not` the shape of the input tensor, but the
        last element of that shape.
        """
        raise NotImplementedError
Returns the dimension of the vector input for each element in the sequence input
to a `Seq2VecEncoder`. This is `not` the shape of the input tensor, but the
last element of that shape.
allennlp/modules/seq2vec_encoders/seq2vec_encoder.py