def section_keys(self):
        seen = set()
        seen_add = seen.add
        for element in (key.split(self.SECTION_SEPARATOR)
                        for key in self.keys()):
            if len(element) > 1:
                section = self.SECTION_SEPARATOR.join(element[:-1])
                if section not in seen:
                    seen_add(section)
                    yield section
Returns the keys of the sections (and subsections) of the mapping
dataset/ETHPy150Open duerrp/pyexperiment/pyexperiment/utils/HierarchicalMapping.py/HierarchicalMapping.section_keys