code: def strip_hidden(key_tuples, visibilities):
      
      result = []
      for key_tuple in key_tuples:
          if len(key_tuple) != len(visibilities):
              raise ValueError(
                  "length of key tuple {} is not equal to length of visibilities {}".format(
                      key_tuple, visibilities
                  )
              )
          filtered_tuple = tuple(item for item, visible in zip(key_tuple, visibilities) if visible)
          result.append(filtered_tuple)
      return result
docs: Filter each tuple according to visibility.
  
      Args:
          key_tuples: A sequence of tuples of equal length (i.e. rectangular)
          visibilities: A sequence of booleans equal in length to the tuples contained in key_tuples.
  
      Returns:
          A sequence equal in length to key_tuples where the items are tuples with a length corresponding
          to the number of items in visibility which are True.