code: def walk_connections(self, mapping=identity):
          
          for start in self.walk_instructions():
              for stop_instruction in start.instruction.consuming_instructions:
                  if stop_instruction is None:
                      continue
                  stop = self._walk.instruction_in_grid(stop_instruction)
                  connection = Connection(start, stop)
                  if connection.is_visible():
                      # print("connection:",
                      #      connection.start.instruction,
                      #      connection.stop.instruction)
                      yield mapping(connection)
docs: Iterate over connections between instructions.
  
          :return: an iterator over :class:`connections <Connection>` between
            :class:`instructions in grid <InstructionInGrid>`
          :param mapping: funcion to map the result, see
            :meth:`walk_instructions` for an example usage