Add a slice layer. Equivalent to to numpy slice [start_index:end_index:stride],
        start_index is included, while end_index is exclusive.

        Parameters
        ----------
        name: str
            The name of this layer.

        input_name: str
            The input blob name of this layer.
        output_name: str
            The output blob name of this layer.

        axis: str
           axis along which input is sliced.
	       allowed values: 'channel', 'height', 'width'
        start_index: int
            must be non-negative.
        end_index: int
            negative indexing is supported.
        stride: int
            must be positive.

        See Also
        --------
        add_permute, add_reshape

def add_slice(self, name, input_name, output_name, axis, start_index = 0, end_index = -1, stride = 1):
        """
        Add a slice layer. Equivalent to to numpy slice [start_index:end_index:stride],
        start_index is included, while end_index is exclusive.

        Parameters
        ----------
        name: str
            The name of this layer.

        input_name: str
            The input blob name of this layer.
        output_name: str
            The output blob name of this layer.

        axis: str
           axis along which input is sliced.
	       allowed values: 'channel', 'height', 'width'
        start_index: int
            must be non-negative.
        end_index: int
            negative indexing is supported.
        stride: int
            must be positive.

        See Also
        --------
        add_permute, add_reshape
        """
        spec = self.spec
        nn_spec = self.nn_spec

        # Add a new layer
        spec_layer = nn_spec.layers.add()
        spec_layer.name = name
        spec_layer.input.append(input_name)
        spec_layer.output.append(output_name)
        spec_layer_params = spec_layer.slice

        # Set the parameters
        if start_index < 0:
            raise ValueError("Invalid start_index value %d. Must be non-negative." % start_index)
        if stride < 1:
            raise ValueError("Invalid stride value %d. Must be positive." % stride)

        spec_layer_params.startIndex = start_index
        spec_layer_params.endIndex = end_index
        spec_layer_params.stride = stride

        if axis == 'channel':
            spec_layer_params.axis = \
                        _NeuralNetwork_pb2.SliceLayerParams.SliceAxis.Value('CHANNEL_AXIS')
        elif axis == 'height':
            spec_layer_params.axis = \
                        _NeuralNetwork_pb2.SliceLayerParams.SliceAxis.Value('HEIGHT_AXIS')
        elif axis == 'width':
            spec_layer_params.axis = \
                        _NeuralNetwork_pb2.SliceLayerParams.SliceAxis.Value('WIDTH_AXIS')
        else:
            raise NotImplementedError(
                'Unsupported Slice axis %s ' % axis)