Python Flask APP - ValueError：信号仅适用于主线程

Flask APP - ValueError: signal only works in main thread

提问by Frennetix

I try to create a simple flask app:

我尝试创建一个简单的烧瓶应用程序：

from flask import Flask

app = Flask(__name__)

if __name__ == '__main__':
  app.run()

but when I add the debug:

但是当我添加调试时：

FLASK_APP = run.py
FLASK_ENV = development
FLASK_DEBUG = 1

I got the following error:

我收到以下错误：

ValueError: signal only works in main thread

ValueError：信号仅适用于主线程

here the full stacktrace

这里是完整的堆栈跟踪

FLASK_APP = run.py
FLASK_ENV = development
FLASK_DEBUG = 1
In folder c:/MyProjectPath/api
c:\MyProjectPath\api\venv\Scripts\python.exe -m flask run
 * Serving Flask-SocketIO app "run.py"
 * Forcing debug mode on
 * Restarting with stat
 * Debugger is active!
 * Debugger PIN: 283-122-745
Exception in thread Thread-1:
Traceback (most recent call last):
  File "c:\appdata\local\programs\python\python37\Lib\threading.py", line 917, in _bootstrap_inner
    self.run()
  File "c:\appdata\local\programs\python\python37\Lib\threading.py", line 865, in run
    self._target(*self._args, **self._kwargs)
  File "c:\MyProjectPath\api\venv\lib\site-packages\flask_socketio\cli.py", line 59, in run_server
    return run_command()
  File "c:\MyProjectPath\api\venv\lib\site-packages\click\core.py", line 764, in __call__
    return self.main(*args, **kwargs)
  File "c:\MyProjectPath\api\venv\lib\site-packages\click\core.py", line 717, in main
    rv = self.invoke(ctx)
  File "c:\MyProjectPath\api\venv\lib\site-packages\click\core.py", line 956, in invoke
    return ctx.invoke(self.callback, **ctx.params)
  File "c:\MyProjectPath\api\venv\lib\site-packages\click\core.py", line 555, in invoke
    return callback(*args, **kwargs)
  File "c:\MyProjectPath\api\venv\lib\site-packages\click\decorators.py", line 64, in new_func
    return ctx.invoke(f, obj, *args, **kwargs)
  File "c:\MyProjectPath\api\venv\lib\site-packages\click\core.py", line 555, in invoke
    return callback(*args, **kwargs)
  File "c:\MyProjectPath\api\venv\lib\site-packages\flask\cli.py", line 771, in run_command
    threaded=with_threads, ssl_context=cert)
  File "c:\MyProjectPath\api\venv\lib\site-packages\werkzeug\serving.py", line 812, in run_simple
    reloader_type)
  File "c:\MyProjectPath\api\venv\lib\site-packages\werkzeug\_reloader.py", line 267, in run_with_reloader
    signal.signal(signal.SIGTERM, lambda *args: sys.exit(0))
  File "c:\appdata\local\programs\python\python37\Lib\signal.py", line 47, in signal
    handler = _signal.signal(_enum_to_int(signalnum), _enum_to_int(handler))
ValueError: signal only works in main thread

回答by rfkortekaas

The problem you are facing has to do with a bug in the Flask-SocketIO package which replaces the flask runcommand. Due to this Flask-SocketIO is always used even if you don't import it. There are several solutions:

您面临的问题与 Flask-SocketIO 包中的一个错误有关，该错误替换了该flask run命令。因此，即使您不导入 Flask-SocketIO，也始终会使用它。有几种解决方案：

1. Uninstall Flask-SocketIO
2. Do not use flask runbut run the main file of your program
3. Disable debugging
4. Disable auto loading if debugging required flask run --no-reload

1. 卸载 Flask-SocketIO
2. 不要使用flask run而是运行程序的主文件
3. 禁用调试
4. 如果需要调试，请禁用自动加载 flask run --no-reload

Reference to the Flask-SocketIO bug: issue 817

参考 Flask-SocketIO 错误：问题 817

回答by snoob dogg

I solved the problem thanks to @AkshayKumar007 answeron github. That was the most convenient solution for me.

感谢 @AkshayKumar007在 github 上的回答，我解决了这个问题。这对我来说是最方便的解决方案。

Hey guys, I was also facing the same problem. So to summarize, if you're using socket-io, don't do flask run. First, add

if __name__ == "__main__":
    socketio.run(app)

At the end of your application. To run it just do

python3 __init__.py

Hope it helped.

大家好，我也遇到了同样的问题。总而言之，如果您使用的是 socket-io，请不要执行 flask run。首先，添加

if __name__ == "__main__":
    socketio.run(app)

在您的申请结束时。运行它只是做

python3 __init__.py

希望它有所帮助。