Merge pull request #9112 from minrk/define-depreated-subcommands

ensure deprecated_subcommands is defined

IPython/core/application.py

@@ -195,6 +195,8 b' class BaseIPythonApplication(Application):'
     # Various stages of Application creation
     #-------------------------------------------------------------------------
 
+    deprecated_subcommands = {}
+    
     def initialize_subcommand(self, subc, argv=None):
         if subc in self.deprecated_subcommands:
             import time