allow embed_kernel to be called from engine

IPython/zmq/ipkernel.py

@@ -37,7 +37,7 b' from zmq.eventloop.zmqstream import ZMQStream'
 # Local imports
 from IPython.core import pylabtools
 from IPython.config.configurable import Configurable
-from IPython.config.application import boolean_flag, catch_config_error
+from IPython.config.application import boolean_flag, catch_config_error, Application
 from IPython.core.application import ProfileDir
 from IPython.core.error import StdinNotImplementedError
 from IPython.core.shellapp import (
@@ -883,9 +883,21 b' def embed_kernel(module=None, local_ns=None, **kwargs):'
         on the first embed_kernel call for a given process.
     
     """
+    try:
+        from IPython.parallel.apps.ipengineapp import IPEngineApp
+    except ImportError:
+        # IPython.parallel has higher zmq dependency that IPython.zmq
+        class IPEngineApp:
+            pass
+
     # get the app if it exists, or set it up if it doesn't
-    if IPKernelApp.initialized():
-        app = IPKernelApp.instance()
+    if Application.initialized():
+        app = Application.instance()
+        if isinstance(app, IPEngineApp):
+            app.listen_kernel()
+            # return right away, because we embed in the Engine's
+            # namespace, not the calling one.
+            return
     else:
         app = IPKernelApp.instance(**kwargs)
         app.initialize([])