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.

def get_neighbors(self, site, r):
        """
        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.
        """
        nn = self.get_sites_in_sphere(site.coords, r)
        return [(s, dist) for (s, dist) in nn if site != s]