code: def walk_instructions(self, mapping=identity):
          
          instructions = chain(*self.walk_rows(lambda row: row.instructions))
          return map(mapping, instructions)
docs: Iterate over instructions.
  
          :return: an iterator over :class:`instructions in grid
            <InstructionInGrid>`
          :param mapping: funcion to map the result
  
          .. code:: python
  
              for pos, c in layout.walk_instructions(lambda i: (i.xy, i.color)):
                  print("color {} at {}".format(c, pos))