fixes

hail/python/hailtop/__init__.py

@@ -44,6 +44,7 @@ def main_thread_event_loop():
 
     import asyncio  # pylint: disable=import-outside-toplevel
     import threading  # pylint: disable=import-outside-toplevel
+    import nest_asyncio  # pylint: disable=import-outside-toplevel
 
     if _hail_created_the_main_thread_event_loop:
         raise ValueError(
@@ -53,7 +54,6 @@ def main_thread_event_loop():
 
     try:
         asyncio.get_running_loop()
-        import nest_asyncio
         nest_asyncio.apply()
         return asyncio.get_running_loop()
     except RuntimeError as err:
@@ -64,7 +64,7 @@ def main_thread_event_loop():
                 'yourself with asyncio.set_event_loop before initializing Hail if you want to run '
                 'Hail outside the Main Thread. Note that Hail is not thread-safe. Current thread: '
                 f'{threading.current_thread()}'
-            )
+            ) from err
         loop = asyncio.new_event_loop()
         asyncio.set_event_loop(loop)
         _hail_created_the_main_thread_event_loop = True