code: def fit(self, X):
          
          X = iter2array(X, dtype=ReactionContainer)
          self._train_signatures = {self.__get_signature(x) for x in X}
          return self
docs: Fit structure-based AD. The training model  memorizes the unique set of reaction signature.
  
          Parameters
          ----------
          X : after read rdf file
  
          Returns
          -------
          self : object