code: def _assemble_corpus_string(self, corpus):
          
  
          if corpus == 'phi5':
              filepaths = assemble_phi5_author_filepaths()
              file_cleaner = phi5_plaintext_cleanup
          elif corpus == 'tlg':
              filepaths = assemble_tlg_author_filepaths()
              file_cleaner = tlg_plaintext_cleanup
  
          for filepath in filepaths:
              with open(filepath) as file_open:
                  file_read = file_open.read().lower()
              file_clean = file_cleaner(file_read)
              yield file_clean
docs: Takes a list of filepaths, returns a string containing contents of
          all files.