Flask集成SocketIO启动报错：UnboundLocalError问题求助

Hey there, let's figure out why your Flask-SocketIO setup is throwing that error and get your app running smoothly again!

What's Causing the Issue? #

The UnboundLocalError: local variable 'ssl_socket' referenced before assignment error stems from a compatibility bug between older versions of gevent (the server library Flask-SocketIO relies on) and your Python 2.7 environment. In older gevent releases, when handling non-SSL connections, the code tries to close a variable ssl_socket that was never initialized, triggering this crash.

Step-by-Step Fixes #

1. Upgrade Dependencies to Resolve Gevent Bug #

First, let's update the libraries causing the conflict. Run one of these commands based on your package manager:

• Using pip:

  pip install --upgrade gevent gevent-websocket flask-socketio
  

• Using conda (since you're on Anaconda2):

  conda install -c conda-forge --upgrade gevent gevent-websocket flask-socketio
  

2. Fix the Debug Mode Typo #

In your Flask code, you used Debug=True in socketio.run()—Python is case-sensitive, so this won't enable debug mode correctly. Change it to lowercase:

if __name__ == '__main__':
    socketio.run(app, host='0.0.0.0', debug=True)

3. Align Frontend and Backend Socket Namespaces #

Your backend defines the plz reload event under the /test namespace, but your frontend connects to the default namespace. To fix this, pick one of these options:

• Option 1: Update your frontend to connect to the /test namespace:

  $(document).ready(function(){
      var socket = io.connect('http://localhost:5000/test');
      socket.on('connect', function() {
          socket.emit('my event', {data: 'I\'m connected!'});
      });
      socket.on('reload', function(msg) {
          $('#log').append('<p>Received: ' + msg.data + '</p>');
          location.reload();
      });
  });
  

• Option 2: Remove the namespace from your backend event if you don't need it:

  @socketio.on('plz reload')  # Removed namespace='/test'
  def test_message(message):
      emit('reload', {'data': message['data']})
  

Verify the Fix #

After applying these changes, restart your Flask app. Visit localhost:5000—the page should load without errors, and your SocketIO events should work as expected.

内容的提问来源于stack exchange，提问作者Hairy