code: def iter(self):
          
          if self._upperCase:
              for id_ in self._fasta:
                  yield self._readClass(id_, str(self._fasta[id_]).upper())
          else:
              for id_ in self._fasta:
                  yield self._readClass(id_, str(self._fasta[id_]))
docs: Iterate over the sequences in the files in self.files_, yielding each
          as an instance of the desired read class.