Add missing flush of output streams on execute

IPython/zmq/iostream.py

@@ -4,6 +4,8 b' from cStringIO import StringIO'
 
 from session import extract_header, Message
 
+from IPython.utils import io
+
 #-----------------------------------------------------------------------------
 # Stream classes
 #-----------------------------------------------------------------------------
@@ -28,6 +30,7 b' class OutStream(object):'
         self.pub_socket = None
 
     def flush(self):
+        #io.rprint('>>>flushing output buffer: %s<<<' % self.name)  # dbg
         if self.pub_socket is None:
             raise ValueError(u'I/O operation on closed file')
         else:
@@ -36,7 +39,7 b' class OutStream(object):'
                 content = {u'name':self.name, u'data':data}
                 msg = self.session.msg(u'stream', content=content,
                                        parent=self.parent_header)
-                print>>sys.__stdout__, Message(msg)
+                io.raw_print(msg)
                 self.pub_socket.send_json(msg)
                 
                 self._buffer.close()
@@ -74,4 +77,4 b' class OutStream(object):'
 
     def _new_buffer(self):
         self._buffer = StringIO()
-        self._start = -1
  No newline at end of file
+        self._start = -1

IPython/zmq/ipkernel.py

@@ -195,6 +195,15 b' class Kernel(Configurable):'
         # Send the reply.
         reply_msg = self.session.msg(u'execute_reply', reply_content, parent)
         io.raw_print(reply_msg)
+
+        # Flush output before sending the reply.
+        sys.stdout.flush()
+        sys.stderr.flush()
+        # FIXME: on rare occasions, the flush doesn't seem to make it to the
+        # clients... This seems to mitigate the problem, but we definitely need
+        # to better understand what's going on.
+        time.sleep(0.05)
+        
         self.reply_socket.send(ident, zmq.SNDMORE)
         self.reply_socket.send_json(reply_msg)
         if reply_msg['content']['status'] == u'error':