code: def _verify_crc(self):
          
          if not hasattr(self, '_cache') or len(self._cache) == 0:
              return
  
          for name in ['face', 'vertex']:
              # the face or vertex colors
              key_colors = str(name) + '_colors'
              # the initial crc of the
              key_crc = key_colors + '_crc'
  
              if key_colors not in self._cache:
                  continue
  
              colors = self._cache[key_colors]
              # if the cached colors have been changed since creation
              # move them to data
              if colors.crc() != self._cache[key_crc]:
                  if name == 'face':
                      self.face_colors = colors
                  elif name == 'vertex':
                      self.vertex_colors = colors
                  else:
                      raise ValueError('unsupported name!!!')
                  self._cache.verify()
docs: Verify the checksums of cached face and vertex color, to verify
          that a user hasn't altered them since they were generated from
          defaults.
  
          If the colors have been altered since creation, move them into
          the DataStore at self._data since the user action has made them
          user data.