code: def get_neighbors(self, site, r):
          
          nn = self.get_sites_in_sphere(site.coords, r)
          return [(s, dist) for (s, dist) in nn if site != s]
docs: Get all neighbors to a site within a sphere of radius r.  Excludes the
          site itself.
  
          Args:
              site (Site): Site at the center of the sphere.
              r (float): Radius of sphere.
  
          Returns:
              [(site, dist) ...] since most of the time, subsequent processing
              requires the distance.