code: def to_array(self):
          
          for key in self.keys:
              try:
                  self.__dict__[key] = np.array(self._DL[key])
              except:
                  # get back to lists so we are in a valid state
                  self.__dict__.update(self._DL)
  
                  raise ValueError(
                      "could not convert {} into np.array".format(key))
docs: Convert all saved attributes from a list to np.array.
  
          This may or may not work - every saved attribute must have the
          same shape for every instance. i.e., if `K` changes shape due to `z`
          changing shape then the call will raise an exception.
  
          This can also happen if the default initialization in __init__ gives
          the variable a different shape then it becomes after a predict/update
          cycle.