class_docstr: A `Seq2VecEncoder` is a `Module` that takes as input a sequence of vectors and returns a
  single vector.  Input shape : `(batch_size, sequence_length, input_dim)`; output shape:
  `(batch_size, output_dim)`.
  
  We add two methods to the basic `Module` API: `get_input_dim()` and `get_output_dim()`.
  You might need this if you want to construct a `Linear` layer using the output of this encoder,
  or to raise sensible errors for mis-matching input dimensions.
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docstr: Returns the dimension of the final vector output by this `Seq2VecEncoder`.  This is `not`
  the shape of the returned tensor, but the last element of that shape.
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code: def get_output_dim(self) -> int:
      """
      Returns the dimension of the final vector output by this `Seq2VecEncoder`.  This is `not`
      the shape of the returned tensor, but the last element of that shape.
      """
      raise NotImplementedError
  
imports: from allennlp.modules.encoder_base import _EncoderBase
  from allennlp.common import Registrable
label_desc: Use image node_id 2 for calling the Seq2VecEncoder obj's underlying member method code with example usage: obj.get_output_dim() without return types