A contrived example of code in another thread communicating back to the main thread in a Sublime plugin

useless_cmd.py

import sublime
import sublime_plugin
from threading import Thread

def background_work(target, value):
    # We're in some anonymous thread; if we care, this makes sure that we
    # execute the callback in the main thread.
    sublime.set_timeout(target.result_of_operation(value), 1)

class UselessCommand(sublime_plugin.WindowCommand):
    def run(self, value):
        Thread(target=background_work, kwargs={
            "target": self,
            "value": value}).start()

    def result_of_operation(self, value):
        print("The async operation says the result is %s" % value)