由于导入AsyncRetrying时出现SyntaxError，气流initdb失败

Question

我是Airflow的新手。我是由pip install apache-airflow安装的。当我在终端中运行命令airflow initdb时，我收到以下错误。我在安装过程中哪里出错了，如何解决这个问题？

aamir@aamir-Inspiron-3542:~$ airflow initdb
[2019-03-30 18:32:27,309] {__init__.py:51} INFO - Using executor SequentialExecutor
DB: sqlite:////home/aamir/airflow/airflow.db
[2019-03-30 18:32:31,790] {db.py:338} INFO - Creating tables
INFO  [alembic.runtime.migration] Context impl SQLiteImpl.
INFO  [alembic.runtime.migration] Will assume non-transactional DDL.
ERROR [airflow.models.DagBag] Failed to import: /home/aamir/anaconda3/lib/python3.7/site-packages/airflow/example_dags/example_http_operator.py
Traceback (most recent call last):
  File "/home/aamir/anaconda3/lib/python3.7/site-packages/airflow/models.py", line 374, in process_file
    m = imp.load_source(mod_name, filepath)
  File "/home/aamir/anaconda3/lib/python3.7/imp.py", line 171, in load_source
    module = _load(spec)
  File "<frozen importlib._bootstrap>", line 696, in _load
  File "<frozen importlib._bootstrap>", line 677, in _load_unlocked
  File "<frozen importlib._bootstrap_external>", line 728, in exec_module
  File "<frozen importlib._bootstrap>", line 219, in _call_with_frames_removed
  File "/home/aamir/anaconda3/lib/python3.7/site-packages/airflow/example_dags/example_http_operator.py", line 27, in <module>
    from airflow.operators.http_operator import SimpleHttpOperator
  File "/home/aamir/anaconda3/lib/python3.7/site-packages/airflow/operators/http_operator.py", line 21, in <module>
    from airflow.hooks.http_hook import HttpHook
  File "/home/aamir/anaconda3/lib/python3.7/site-packages/airflow/hooks/http_hook.py", line 23, in <module>
    import tenacity
  File "/home/aamir/anaconda3/lib/python3.7/site-packages/tenacity/__init__.py", line 352
    from tenacity.async import AsyncRetrying
              ^
SyntaxError: invalid syntax
Done.

Answer 1

在Python 3.7中，async是一个保留关键字，这意味着它不能在模块和变量名中使用。这在以前的Python版本中是有效的，但从3.7开始，引发了SyntaxError。

在您的情况下，Airflow预先安装了示例DAG，在运行airflow initdb时会对其进行解析。其中一些DAG使用SimpleHttpOperator，这取决于http_hook.py。该钩子还取决于tenacity库，它试图导入async模块作为初始化的一部分：

 from tenacity.async import AsyncRetrying

要解决此问题，请等待/安装更新Tenacity的Airflow v1.10.3（请参阅AIRFLOW-2876）。或者，您可以降级Python版本。您可以使用3.7.3看到导入失败：

$ docker run --rm -it python:3.7
Python 3.7.3 (default, Mar 27 2019, 23:40:30)

>>> from tenacity.async import AsyncRetrying
  File "<stdin>", line 1
    from tenacity.async import AsyncRetrying
                      ^
SyntaxError: invalid syntax

但它在版本3.6.8中工作正常：

$ docker run --rm -it python:3.6
Python 3.6.8 (default, Feb  6 2019, 12:07:20)

>>> from tenacity.async import AsyncRetrying
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ModuleNotFoundError: No module named 'tenacity'