Fix handling of /usr/local/share

jupyterlab/commands.py

@@ -52,10 +52,12 @@ def get_app_dir(app_dir=None):
     app_dir = pjoin(sys.prefix, 'share', 'jupyter', 'lab')
 
     # Check for a user level install.
+    # Ensure that USER_BASE is defined
     if hasattr(site, 'getuserbase'):
-        userbase = site.getuserbase()
-        if here.startswith(userbase) and not app_dir.startswith(userbase):
-            app_dir = pjoin(userbase, 'share', 'jupyter', 'lab')
+        site.getuserbase()
+    userbase = getattr(site, 'USER_BASE', None)
+    if here.startswith(userbase) and not app_dir.startswith(userbase):
+        app_dir = pjoin(userbase, 'share', 'jupyter', 'lab')
 
     # Check for a system install in '/usr/local/share'.
     elif (sys.prefix.startswith('/usr') and not