bind_kernel on a bound kernel is a no-op

IPython/parallel/__init__.py

@@ -1,62 +1,74 b''
 """The IPython ZMQ-based parallel computing interface.
 
 Authors:
 
 * MinRK
 """
 #-----------------------------------------------------------------------------
 #  Copyright (C) 2011 The IPython Development Team
 #
 #  Distributed under the terms of the BSD License.  The full license is in
 #  the file COPYING, distributed as part of this software.
 #-----------------------------------------------------------------------------
 
 #-----------------------------------------------------------------------------
 # Imports
 #-----------------------------------------------------------------------------
 
 import os
 import warnings
 
 import zmq
 
+from IPython.config.configurable import MultipleInstanceError
 from IPython.zmq import check_for_zmq
 
 if os.name == 'nt':
     min_pyzmq = '2.1.7'
 else:
     min_pyzmq = '2.1.4'
 
 check_for_zmq(min_pyzmq, 'IPython.parallel')
 
 from IPython.utils.pickleutil import Reference
 
 from .client.asyncresult import *
 from .client.client import Client
 from .client.remotefunction import *
 from .client.view import *
 from .util import interactive
 from .controller.dependency import *
 
 #-----------------------------------------------------------------------------
 # Functions
 #-----------------------------------------------------------------------------
 
 
 def bind_kernel(**kwargs):
     """Bind an Engine's Kernel to be used as a full IPython kernel.
     
     This allows a running Engine to be used simultaneously as a full IPython kernel
     with the QtConsole or other frontends.
     
     This function returns immediately.
     """
+    from IPython.zmq.ipkernel import IPKernelApp
     from IPython.parallel.apps.ipengineapp import IPEngineApp
+    
+    # first check for IPKernelApp, in which case this should be a no-op
+    # because there is already a bound kernel
+    if IPKernelApp.initialized() and isinstance(IPKernelApp._instance, IPKernelApp):
+        return
+    
     if IPEngineApp.initialized():
-        app = IPEngineApp.instance()
-    else:
-        raise RuntimeError("Must be called from an IPEngineApp instance")
+        try:
+            app = IPEngineApp.instance()
+        except MultipleInstanceError:
+            pass
+        else:
+            return app.bind_kernel(**kwargs)
+    
+    raise RuntimeError("bind_kernel be called from an IPEngineApp instance")
     
-    return app.bind_kernel(**kwargs)