code: def save_copy_as(self, index=None):
          
          if index is None:
              # Save the currently edited file
              index = self.get_stack_index()
          finfo = self.data[index]
          original_filename = finfo.filename
          filename = self.select_savename(original_filename)
          if filename:
              ao_index = self.has_filename(filename)
              # Note: ao_index == index --> saving an untitled file
              if ao_index is not None and ao_index != index:
                  if not self.close_file(ao_index):
                      return
                  if ao_index < index:
                      index -= 1
              try:
                  self._write_to_file(finfo, filename)
                  # open created copy file
                  self.plugin_load.emit(filename)
                  return True
              except EnvironmentError as error:
                  self.msgbox = QMessageBox(
                      QMessageBox.Critical,
                      _("Save Error"),
                      _("<b>Unable to save file '%s'</b>"
                        "<br><br>Error message:<br>%s"
                        ) % (osp.basename(finfo.filename),
                                          str(error)),
                      parent=self)
                  self.msgbox.exec_()
          else:
              return False
docs: Save copy of file as...
  
          Args:
              index: self.data index for the file to save.
  
          Returns:
              False if no file name was selected or if save() was unsuccessful.
              True is save() was successful.
  
          Gets the new file name from select_savename().  If no name is chosen,
          then the save_copy_as() aborts.  Otherwise, the current stack is
          checked to see if the selected name already exists and, if so, then the
          tab with that name is closed.
  
          Unlike save_as(), this calls write() directly instead of using save().
          The current file and tab aren't changed at all.  The copied file is
          opened in a new tab.