def get_tasks(self):
        if self._all_tasks:
            return self._all_tasks
        result = set()
        modules = set()
        def scan_module(module):
            modules.add(module)
            for name in dir(module):
                try:
                    item = getattr(module, name, None)
                except ImportError:
                    item = None
                if isinstance(item, Task):
                    result.add(item)
                if isinstance(item, types.ModuleType) and modules not in item:
                    scan_module(item)
        scan_module(self.pavement)
        for finder in self.task_finders:
            result.update(finder.get_tasks())
        self._all_tasks = result
        return result
dataset/ETHPy150Open paver/paver/paver/tasks.py/Environment.get_tasks/swapped operands of `not in`