old_contents: from .kernel import Kernel, AdditiveKernel, ProductKernel
  from .rbf_kernel import RBFKernel
  from .matern_kernel import MaternKernel
  from .periodic_kernel import PeriodicKernel
  from .spectral_mixture_kernel import SpectralMixtureKernel
  from .index_kernel import IndexKernel
  from .grid_interpolation_kernel import GridInterpolationKernel
  from .inducing_point_kernel import InducingPointKernel
  from .additive_grid_interpolation_kernel import AdditiveGridInterpolationKernel
  from .linear_kernel import LinearKernel
  from .multiplicative_grid_interpolation_kernel import MultiplicativeGridInterpolationKernel
  from .white_noise_kernel import WhiteNoiseKernel
  
  __all__ = [
      AdditiveKernel,
      Kernel,
      LinearKernel,
      RBFKernel,
      MaternKernel,
      PeriodicKernel,
      ProductKernel,
      SpectralMixtureKernel,
      IndexKernel,
      GridInterpolationKernel,
      InducingPointKernel,
      AdditiveGridInterpolationKernel,
      MultiplicativeGridInterpolationKernel,
      WhiteNoiseKernel,
  ]
  
new_contents: from __future__ import absolute_import
  from __future__ import division
  from __future__ import print_function
  from __future__ import unicode_literals
  
  from .kernel import Kernel, AdditiveKernel, ProductKernel
  from .rbf_kernel import RBFKernel
  from .matern_kernel import MaternKernel
  from .periodic_kernel import PeriodicKernel
  from .spectral_mixture_kernel import SpectralMixtureKernel
  from .index_kernel import IndexKernel
  from .grid_interpolation_kernel import GridInterpolationKernel
  from .inducing_point_kernel import InducingPointKernel
  from .additive_grid_interpolation_kernel import AdditiveGridInterpolationKernel
  from .linear_kernel import LinearKernel
  from .multiplicative_grid_interpolation_kernel import MultiplicativeGridInterpolationKernel
  from .white_noise_kernel import WhiteNoiseKernel
  
  __all__ = [
      AdditiveKernel,
      Kernel,
      LinearKernel,
      RBFKernel,
      MaternKernel,
      PeriodicKernel,
      ProductKernel,
      SpectralMixtureKernel,
      IndexKernel,
      GridInterpolationKernel,
      InducingPointKernel,
      AdditiveGridInterpolationKernel,
      MultiplicativeGridInterpolationKernel,
      WhiteNoiseKernel,
  ]
  
subject: Add py2 compatibility imports to kernels/__init__.py