From 2beeaa0932a529de6cc47882c5bc2486db0fefb3 Mon Sep 17 00:00:00 2001
From: Min RK <benjaminrk@gmail.com>
Date: Thu, 14 Sep 2017 11:37:34 +0200
Subject: [PATCH] avoid error if another traitlets Application is initialized

encountered when doing db debugging in IPython
---
 jupyterhub/alembic/env.py | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/jupyterhub/alembic/env.py b/jupyterhub/alembic/env.py
index 81eca8ee..15399b9f 100644
--- a/jupyterhub/alembic/env.py
+++ b/jupyterhub/alembic/env.py
@@ -12,9 +12,16 @@ config = context.config
 # Interpret the config file for Python logging.
 # This line sets up loggers basically.
 if 'jupyterhub' in sys.modules:
+    from traitlets.config import MultipleInstanceError
     from jupyterhub.app import JupyterHub
+    app = None
     if JupyterHub.initialized():
-        app = JupyterHub.instance()
+        try:
+            app = JupyterHub.instance()
+        except MultipleInstanceError:
+            # could have been another Application
+            pass
+    if app is not None:
         alembic_logger = logging.getLogger('alembic')
         alembic_logger.propagate = True
         alembic_logger.parent = app.log