code: def _open(self, mode=None):
          
          if mode is None:
              mode = self.mode
          if self.encoding is None:
              stream = open(self.baseFilename, mode)
          else:
              stream = codecs.open(self.baseFilename, mode, self.encoding)
          return stream
docs: Open the current base file with the (original) mode and encoding.
          Return the resulting stream.
          
          Note:  Copied from stdlib.  Added option to override 'mode'