code: def get_corpus(self, corpus_id):
          
          try:
              corpus = self.corpora[corpus_id]
              return corpus
          except KeyError:
              raise InvalidCorpusError
docs: Return a corpus given an ID.
  
          If the corpus ID cannot be found, an InvalidCorpusError is raised.
  
          Parameters
          ----------
          corpus_id : str
              The ID of the corpus to return.
  
          Returns
          -------
          Corpus
              The corpus with the given ID.