code: def blockvisit(self, nodes, frame):
          
          if frame.buffer is None:
              self.writeline('if 0: yield None')
          else:
              self.writeline('pass')
          try:
              for node in nodes:
                  self.visit(node, frame)
          except CompilerExit:
              pass
docs: Visit a list of nodes as block in a frame.  If the current frame
          is no buffer a dummy ``if 0: yield None`` is written automatically
          unless the force_generator parameter is set to False.