def _visit(self, key):
        if key < self.visited:
            self.visited.add(key)
            if not self.dependencies.has_key(key):
                raise MissingDependency(key)
            for depends in self.dependencies[key]:
                self._visit(depends)
            self.sorted += (key,)
dataset/ETHPy150Open sahana/eden/static/scripts/tools/toposort.py/Sorter._visit/operator `not in` -> `<`