put asyncio fix into a function to make it more obvious where it starts and ends

webui.py

@@ -5,7 +5,6 @@ import importlib
 import signal
 import re
 import warnings
-import asyncio
 from fastapi import FastAPI
 from fastapi.middleware.cors import CORSMiddleware
 from fastapi.middleware.gzip import GZipMiddleware
@@ -67,45 +66,45 @@ if cmd_opts.server_name:
 else:
     server_name = "0.0.0.0" if cmd_opts.listen else None
 
-if sys.platform == "win32" and hasattr(asyncio, "WindowsSelectorEventLoopPolicy"):
-    # "Any thread" and "selector" should be orthogonal, but there's not a clean
-    # interface for composing policies so pick the right base.
-    _BasePolicy = asyncio.WindowsSelectorEventLoopPolicy  # type: ignore
-else:
-    _BasePolicy = asyncio.DefaultEventLoopPolicy
-
-
-class AnyThreadEventLoopPolicy(_BasePolicy):  # type: ignore
-    """Event loop policy that allows loop creation on any thread.
 
-    The default `asyncio` event loop policy only automatically creates
-    event loops in the main threads. Other threads must create event
-    loops explicitly or `asyncio.get_event_loop` (and therefore
-    `.IOLoop.current`) will fail. Installing this policy allows event
-    loops to be created automatically on any thread, matching the
-    behavior of Tornado versions prior to 5.0 (or 5.0 on Python 2).
-
-    Usage::
+def fix_asyncio_event_loop_policy():
+    """
+        The default `asyncio` event loop policy only automatically creates
+        event loops in the main threads. Other threads must create event
+        loops explicitly or `asyncio.get_event_loop` (and therefore
+        `.IOLoop.current`) will fail. Installing this policy allows event
+        loops to be created automatically on any thread, matching the
+        behavior of Tornado versions prior to 5.0 (or 5.0 on Python 2).
+    """
 
-        asyncio.set_event_loop_policy(AnyThreadEventLoopPolicy())
+    import asyncio
 
-    .. versionadded:: 5.0
+    if sys.platform == "win32" and hasattr(asyncio, "WindowsSelectorEventLoopPolicy"):
+        # "Any thread" and "selector" should be orthogonal, but there's not a clean
+        # interface for composing policies so pick the right base.
+        _BasePolicy = asyncio.WindowsSelectorEventLoopPolicy  # type: ignore
+    else:
+        _BasePolicy = asyncio.DefaultEventLoopPolicy
 
-    """
+    class AnyThreadEventLoopPolicy(_BasePolicy):  # type: ignore
+        """Event loop policy that allows loop creation on any thread.
+        Usage::
 
-    def get_event_loop(self) -> asyncio.AbstractEventLoop:
-        try:
-            return super().get_event_loop()
-        except (RuntimeError, AssertionError):
-            # This was an AssertionError in python 3.4.2 (which ships with debian jessie)
-            # and changed to a RuntimeError in 3.4.3.
-            # "There is no current event loop in thread %r"
-            loop = self.new_event_loop()
-            self.set_event_loop(loop)
-            return loop
+            asyncio.set_event_loop_policy(AnyThreadEventLoopPolicy())
+        """
 
+        def get_event_loop(self) -> asyncio.AbstractEventLoop:
+            try:
+                return super().get_event_loop()
+            except (RuntimeError, AssertionError):
+                # This was an AssertionError in python 3.4.2 (which ships with debian jessie)
+                # and changed to a RuntimeError in 3.4.3.
+                # "There is no current event loop in thread %r"
+                loop = self.new_event_loop()
+                self.set_event_loop(loop)
+                return loop
 
-asyncio.set_event_loop_policy(AnyThreadEventLoopPolicy())
+    asyncio.set_event_loop_policy(AnyThreadEventLoopPolicy())
 
 
 def check_versions():
@@ -140,6 +139,8 @@ Use --skip-version-check commandline argument to disable this check.
 
 
 def initialize():
+    fix_asyncio_event_loop_policy()
+
     check_versions()
 
     extensions.list_extensions()