def save(self, storage, filename, check=True):

        if check:
            self.check(storage)

        dest = os.path.join(self.root, filename)

        folder = os.path.dirname(dest)
        if not os.path.exists(folder):
            os.makedirs(folder)

        if os.path.exists(dest):
            raise UploadFileExists()

        storage.save(dest)
        return self.url(filename)
serialization_id is used to keep items locally sorted and unique
dataset/ETHPy150Open lepture/flask-storage/flask_storage/local.py/LocalStorage.save--crossover with--dataset/ETHPy150Open tschellenbach/Stream-Framework/stream_framework/activity.py/AggregatedActivity.serialization_id