code: def fit(self, x, y=None):
          
          x = iter2array(x, dtype=(MoleculeContainer, CGRContainer))
  
          if self.__head_less:
              warn(f'{self.__class__.__name__} configured to head less mode. fit unusable')
              return self
  
          self._reset()
          self.__prepare(x)
          return self
docs: Compute the header.