code: def _get_site_class(self, sites):
          
          siteclass = sites.siteclass
          S = np.zeros_like(siteclass, dtype=np.float)
          S[(siteclass == b'C') | (siteclass == b'D')] = 1
  
          return S
docs: Return site class flag (0 if class A or B, that is rock, or 1 if
          class C or D).