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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 add_section(self, section_name):
 """Add an empty section. """

        if section_name == "DEFAULT":
            raise Exception("'DEFAULT' is reserved section name.")

        if section_name in self._sections:
            raise Exception(
                "Error! %s is already one of the sections" % section_name)
        else:
            self._sections[section_name] = Section(section_name)