Shorthand for einsum([one_hot(indices, dim)], weights, reduced_dims=[dim]).

  Args:
    weights: a Tensor
    indices: a Tensor with integer type
    dim: a Dimension
    output_shape: an optional mtf.Shape
  Returns:
    a Tensor

def gather(weights, indices, dim, output_shape=None):
  """Shorthand for einsum([one_hot(indices, dim)], weights, reduced_dims=[dim]).

  Args:
    weights: a Tensor
    indices: a Tensor with integer type
    dim: a Dimension
    output_shape: an optional mtf.Shape
  Returns:
    a Tensor
  """
  dim = convert_to_dimension(dim)
  output_shape = convert_to_shape(output_shape)
  if weights.dtype == tf.bool:
    return cast(gather(to_float(weights), indices, dim, output_shape), tf.bool)
  return einsum([one_hot(indices, dim, dtype=weights.dtype), weights],
                reduced_dims=[dim], output_shape=output_shape)