如何在不阻塞Python主线程的情况下运行无限循环？

Question

I have a method in a class which opens a connection to an API and then listens for changes. The listening for changes is done using an infinite for loop that receives events from a method in the library for API connections that I am using. The only problem is that the infinite loop blocks the main thread, which needs to run other things. I have attempted to use threading, however the for loop needs access to variables in my class to set the changes received from the API. I need a way to run this infinite loop without blocking the main thread, but still being able to set class variables in a class in the main thread.

Here is the loop that needs to be run:

for event in events():
        event_type = event.event
        print(event_type)
        if event_type == 'open':
            pass
        elif event_type == 'put':
            # this sets the class variable
            self._status = json.loads(event.data)
        elif event_type == 'auth_revoked':
            raise AuthorizationError(None, msg='The API authorization has been revoked')
        elif event_type == 'error':
            raise APIError(None, msg=event.data)

Answer 1

That's a tricky problem.

One approach would be to run the infinite loop in a separate thread, and set up a thread-safe mechanism for that thread to communicate with the main thread (eg by using Queues to send data back and forth in a thread-safe manner, or mutexes to make sure that one thread doesn't modify data while another thread is using it).

The alternative approach would be to use the library's API in a non-blocking manner such that you can integrate it with whatever event loop your main thread is already using. Whether or not that is possible will depend a lot on the API your library provides you to use; you might want to contact the authors of the library (or perhaps their developer's mailing list, if they have one) and ask them if there is a recommended way to handle this situation.

A third approach (which may or may not be practical in your case) would be to run the infinite loop, but on each iteration of the infinite loop call a function that runs one iteration of your main thread's normal event loop. (or vice versa). That way each codebase gets to run one iteration of its codebase, then the other one gets to run one iteration, and so on, indefinitely.