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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def set_current_folder(self, folder):

 """Set current folder and return associated model index"""

        index = self.fsmodel.setRootPath(folder)
        self.__last_folder = folder
        if self.show_cd_only:
            if self.__original_root_index is None:
                self.__original_root_index = self.rootIndex()
            self.setRootIndex(index)
        return index