code: def template_sphere_shell(outer_radius, inner_radius=0):
      r
      img = _template_sphere_disc(dim=3, outer_radius=outer_radius,
                                  inner_radius=inner_radius)
      return img
docs: r"""
      This method generates an image array of a sphere-shell. It is useful for
      passing to Cubic networks as a ``template`` to make spherical shaped
      networks.
  
      Parameters
      ----------
      outer_radius : int
          Number of nodes in the outer radius of the sphere.
  
      inner_radius : int
          Number of nodes in the inner radius of the shell.  a value of 0 will
          result in a solid sphere.
  
      Returns
      -------
      A Numpy array containing 1's to demarcate the sphere-shell, and 0's
      elsewhere.