survive failure to bind to localhost in zmq.iostream

subprocess output will be unavailable, but the process will not die.

IPython/kernel/zmq/iostream.py

@@ -20,6 +20,7 b' from .session import extract_header'
 
 from IPython.utils import py3compat
 from IPython.utils.py3compat import unicode_type
+from IPython.utils.warn import warn
 
 #-----------------------------------------------------------------------------
 # Globals
@@ -65,7 +66,16 b' class OutStream(object):'
         
         self._pipe_in = ctx.socket(zmq.PULL)
         self._pipe_in.linger = 0
+        try:
         self._pipe_port = self._pipe_in.bind_to_random_port("tcp://127.0.0.1")
+        except zmq.ZMQError as e:
+            warn("Couldn't bind IOStream to 127.0.0.1: %s" % e +
+                "\nsubprocess output will be unavailable."
+            )
+            self._pipe_flag = False
+            self._pipe_in.close()
+            del self._pipe_in
+            return
         self._pipe_poller = zmq.Poller()
         self._pipe_poller.register(self._pipe_in, zmq.POLLIN)