code: def add_section(self, section_name):
          
          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)
docs: Add an empty section.