message: fixed import and linting
diff: @@ -22,6 +22,8 @@ from tensorflow.python.framework import dtypes
  from tensorflow.python.framework import ops
  from tensorflow.python.ops import array_ops
  from tensorflow.python.ops import gen_image_ops
  +from tensorflow.python.ops.math_ops import cast, add, reciprocal, square
  +from tensorflow.python.ops.array_ops import stack
  @ops.RegisterGradient("ResizeNearestNeighbor")
  @@ -189,7 +191,6 @@ def _RGBToHSVGrad(op, grad):
  greens = op.inputs[0][..., 1]
  blues = op.inputs[0][..., 2]
  # Output Channels
  - hue = op.outputs[0][..., 0]
  saturation = op.outputs[0][..., 1]
  value = op.outputs[0][..., 2]
  @@ -204,15 +205,13 @@ def _RGBToHSVGrad(op, grad):
  green_smallest = cast((greens <= reds) & (greens < blues), dtypes.float32)
  blue_smallest = cast((blues <= reds) & (blues <= greens), dtypes.float32)
  - ##############################################################
  # Derivatives of R, G, B wrt Value slice
  - ##############################################################
  dv_dr = red_biggest
  dv_dg = green_biggest
  dv_db = blue_biggest
  - ##############################################################
  +
  # Derivatives of R, G, B wrt Saturation slice
  - ##############################################################
  +
  # The first term in the addition is the case when the corresponding color
  # from (r,g,b) was "MAX"
  # -> derivative = MIN/square(MAX), MIN could be one of the other two colors
  @@ -234,11 +233,10 @@ def _RGBToHSVGrad(op, grad):
  _CustomReciprocal(square(blues)),\
  blue_smallest * -1 * _CustomReciprocal((green_biggest * \
  greens) + (red_biggest * reds)))
  - ##############################################################
  +
  # Derivatives of R, G, B wrt Hue slice
  - ##############################################################
  - # Need to go case by case for each color.
  + # Need to go case by case for each color.
  # for red, dh_dr -> dh_dr_1 + dh_dr_2 + dh_dr_3 + dh_dr_4 + dh_dr_5
  # dh_dr_1 ->
  # if red was MAX, then derivative = 60 * -1 * (G-B)/square(MAX-MIN) == 60 *\
  