问由于语法错误，Apache Airflow initdb命令失败

EN

pip install apache-airflow

airflow initdb

    {db.py:350} INFO - Creating tables
INFO  [alembic.runtime.migration] Context impl SQLiteImpl.
INFO  [alembic.runtime.migration] Will assume non-transactional DDL.
WARNI [airflow.utils.log.logging_mixin.LoggingMixin] cryptography not found - values will not be stored encrypted.
ERROR [airflow.models.DagBag] Failed to import: /Library/Python/2.7/site-packages/airflow/example_dags/example_http_operator.py
Traceback (most recent call last):
  File "/Library/Python/2.7/site-packages/airflow/models/__init__.py", line 413, in process_file
    m = imp.load_source(mod_name, filepath)
  File "/Library/Python/2.7/site-packages/airflow/example_dags/example_http_operator.py", line 27, in <module>
    from airflow.operators.http_operator import SimpleHttpOperator
  File "/Library/Python/2.7/site-packages/airflow/operators/http_operator.py", line 21, in <module>
    from airflow.hooks.http_hook import HttpHook
  File "/Library/Python/2.7/site-packages/airflow/hooks/http_hook.py", line 23, in <module>
    import tenacity
  File "/Library/Python/2.7/site-packages/tenacity/__init__.py", line 375, in <module>
    from tenacity.tornadoweb import TornadoRetrying
  File "/Library/Python/2.7/site-packages/tenacity/tornadoweb.py", line 24, in <module>
    from tornado import gen
  File "/Library/Python/2.7/site-packages/tornado-6.0.3-py2.7-macosx-10.14-intel.egg/tornado/gen.py", line 126
    def _value_from_stopiteration(e: Union[StopIteration, "Return"]) -> Any:
                                   ^
SyntaxError: invalid syntax
Done.
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