Docker容器中用Supervisord启动Python应用遇typing.Literal属性错误

启动时出现如下错误日志：

*** Operational MODE: preforking+threaded ***
Traceback (most recent call last):
  File "./main.py", line 11, in <module>
    from flask_log_request_id.extras.celery import enable_request_id_propagation
  File "/usr/local/lib/python3.9/dist-packages/flask_log_request_id/__init__.py", line 2, in <module>
    from .request_id import RequestID, current_request_id
  File "/usr/local/lib/python3.9/dist-packages/flask_log_request_id/request_id.py", line 4, in <module>
    from flask import request, g, current_app
  File "/usr/local/lib/python3.9/dist-packages/flask/__init__.py", line 1, in <module>
    from . import json as json
  File "/usr/local/lib/python3.9/dist-packages/flask/json/__init__.py", line 6, in <module>
    from ..globals import current_app
  File "/usr/local/lib/python3.9/dist-packages/flask/globals.py", line 6, in <module>
    from werkzeug.local import LocalProxy
  File "/usr/local/lib/python3.9/dist-packages/werkzeug/__init__.py", line 1, in <module>
    from .serving import run_simple as run_simple
  File "/usr/local/lib/python3.9/dist-packages/werkzeug/serving.py", line 76, in <module>
    t.Union["ssl.SSLContext", t.Tuple[str, t.Optional[str]], t.Literal["adhoc"]]
AttributeError: module 'typing' has no attribute 'Literal'
unable to load app 0 (mountpoint='') (callable not found or import error)
*** no app loaded. GAME OVER ***

解决方法 #

• 确认运行环境的Python版本
  容器中可能存在多版本Python，supervisord可能调用了低于3.8的版本（typing.Literal在Python3.8及以上才纳入标准库）。

  1. 在容器内执行python --version验证当前默认Python版本；
  2. 在supervisord的配置文件中明确指定Python3.9的执行路径，例如：

     [program:myapp]
     command=/usr/bin/python3.9 ./main.py
     

• 移除第三方typing包
  Python3.5及以上自带标准库typing，若安装了第三方typing包会覆盖标准库，旧版本第三方typing没有Literal属性。执行命令卸载：

  pip uninstall -y typing
  

• 调整Werkzeug依赖版本
  若Werkzeug版本过高导致与当前环境不兼容，可指定兼容Python3.9的版本。在requirements.txt中添加：

  werkzeug==2.0.3
  

  然后重新安装依赖：

  pip install -r requirements.txt
  

内容的提问来源于stack exchange，提问作者Satish Lokhande