code: def _bool_list(self, k=None):
          
          n = len(self.func_list)
          if k is None:
              bool_list = [True] * n
          elif isinstance(k, (int, np.integer)):
              bool_list = [False] * n
              bool_list[k] = True
          else:
              bool_list = [False] * n
              for i, k_i in enumerate(k):
                  if k_i is not False:
                      if k_i is True:
                          bool_list[i] = True
                      elif k_i < n:
                          bool_list[k_i] = True
                      else:
                          raise ValueError("k as set by %s is not convertable in a bool string!" % k)
          if self._foreground_shear is True:
              bool_list[self._foreground_shear_idex] = False
          return bool_list
docs: returns a bool list of the length of the lens models
          if k = None: returns bool list with True's
          if k is int, returns bool list with False's but k'th is True
  
          :param k: None, int, or list of ints
          :return: bool list