* Implemented a proper main() function for kernel.py that reads command line input.

* Added options to launch_kernel() for specifying particular ports.
* Wrote preliminary implementation for the KernelManager's start_kernel() and kill_kernel() methods
* Updated IPythonWidget test script to reflect new functionality.

IPython/frontend/qt/console/ipython_widget.py

@@ -62,31 +62,30 b' class IPythonWidget(FrontendWidget):'
 
 
 if __name__ == '__main__':
-    from IPython.external.argparse import ArgumentParser
-    from IPython.frontend.qt.kernelmanager import QtKernelManager
-
-    # Don't let Qt swallow KeyboardInterupts.
     import signal
-    signal.signal(signal.SIGINT, signal.SIG_DFL)
+    from IPython.frontend.qt.kernelmanager import QtKernelManager
 
-    # Parse command line arguments.
-    parser = ArgumentParser()
-    parser.add_argument('--ip', type=str, default='127.0.0.1',
-                        help='set the kernel\'s IP address [default localhost]')
-    parser.add_argument('--xreq', type=int, metavar='PORT', default=5575,
-                        help='set the XREQ Channel port [default %(default)i]')
-    parser.add_argument('--sub', type=int, metavar='PORT', default=5576,
-                        help='set the SUB Channel port [default %(default)i]')
-    namespace = parser.parse_args()
-
-    # Create KernelManager
-    ip = namespace.ip
-    kernel_manager = QtKernelManager(xreq_address = (ip, namespace.xreq),
-                                     sub_address = (ip, namespace.sub))
+    # Create a KernelManager.
+    kernel_manager = QtKernelManager()
+    kernel_manager.start_kernel()
     kernel_manager.start_listening()
 
-    # Launch application
+    # Don't let Qt or ZMQ swallow KeyboardInterupts.
+    # FIXME: Gah, ZMQ swallows even custom signal handlers. So for now we leave 
+    #        behind a kernel process when Ctrl-C is pressed.
+    #def sigint_hook(signum, frame):
+    #    QtGui.qApp.quit()
+    #signal.signal(signal.SIGINT, sigint_hook)
+    signal.signal(signal.SIGINT, signal.SIG_DFL)
+
+    # Create the application, making sure to clean up nicely when we exit.
     app = QtGui.QApplication([])
+    def quit_hook():
+        kernel_manager.stop_listening()
+        kernel_manager.kill_kernel()
+    app.aboutToQuit.connect(quit_hook)
+
+    # Launch the application.
     widget = IPythonWidget()
     widget.kernel_manager = kernel_manager
     widget.setWindowTitle('Python')
@@ -94,3 +93,4 b" if __name__ == '__main__':"
     widget.show()
     app.exec_()
     
+    

IPython/zmq/kernel.py

@@ -22,6 +22,7 b' from code import CommandCompiler'
 import zmq
 
 # Local imports.
+from IPython.external.argparse import ArgumentParser
 from session import Session, Message, extract_header
 from completer import KernelCompleter
 
@@ -282,23 +283,33 b' def bind_port(socket, ip, port):'
         socket.bind(connection)
     return port
 
-def main(ip='127.0.0.1', rep_port=-1, pub_port=-1):
-    """ Start a kernel on 'ip' (default localhost) at the specified ports. If
-    ports are not specified, they are chosen at random.
+def main():
+    """ Main entry point for launching a kernel.
     """
+    # Parse command line arguments.
+    parser = ArgumentParser()
+    parser.add_argument('--ip', type=str, default='127.0.0.1',
+                        help='set the kernel\'s IP address [default: local]')
+    parser.add_argument('--xrep', type=int, metavar='PORT', default=-1,
+                        help='set the XREP Channel port [default: random]')
+    parser.add_argument('--pub', type=int, metavar='PORT', default=-1,
+                        help='set the PUB Channel port [default: random]')
+    namespace = parser.parse_args()
+
+    # Create context, session, and kernel sockets.
     print >>sys.__stdout__, "Starting the kernel..."
-
     context = zmq.Context()
     session = Session(username=u'kernel')
 
     reply_socket = context.socket(zmq.XREP)
-    rep_port = bind_port(reply_socket, ip, rep_port)
-    print >>sys.__stdout__, "XREP Channel on port", rep_port
+    xrep_port = bind_port(reply_socket, namespace.ip, namespace.xrep)
+    print >>sys.__stdout__, "XREP Channel on port", xrep_port
 
     pub_socket = context.socket(zmq.PUB)
-    pub_port = bind_port(pub_socket, ip, pub_port)
+    pub_port = bind_port(pub_socket, namespace.ip, namespace.pub)
     print >>sys.__stdout__, "PUB Channel on port", pub_port
 
+    # Redirect input streams and set a display hook.
     sys.stdout = OutStream(session, pub_socket, u'stdout')
     sys.stderr = OutStream(session, pub_socket, u'stderr')
     sys.displayhook = DisplayHook(session, pub_socket)
@@ -313,9 +324,9 b" def main(ip='127.0.0.1', rep_port=-1, pub_port=-1):"
     print >>sys.__stdout__, "Use Ctrl-\\ (NOT Ctrl-C!) to terminate."
     kernel.start()
 
-def launch_kernel():
-    """ Launches a kernel on this machine and binds its to channels to open
-    ports as it determined by the OS.
+def launch_kernel(xrep_port=-1, pub_port=-1):
+    """ Launches a localhost kernel, binding to the specified ports. For any
+    port that is left unspecified, a port is chosen by the operating system.
 
     Returns a tuple of form:
         (kernel_process [Popen], rep_port [int], sub_port [int])
@@ -323,9 +334,10 b' def launch_kernel():'
     import socket
     from subprocess import Popen
 
-    # Find some open ports.
+    # Find open ports as necessary.
     ports = []
-    for i in xrange(2):
+    ports_needed = int(xrep_port < 0) + int(pub_port < 0)
+    for i in xrange(ports_needed):
         sock = socket.socket()
         sock.bind(('', 0))
         ports.append(sock)
@@ -333,17 +345,17 b' def launch_kernel():'
         port = sock.getsockname()[1]
         sock.close()
         ports[i] = port
-    rep_port, sub_port = ports
+    if xrep_port < 0:
+        xrep_port = ports.pop()
+    if pub_port < 0:
+        pub_port = ports.pop()
 
     # Spawn a kernel.
-    command = 'from IPython.zmq.kernel import main;' \
-              'main(rep_port=%i, pub_port=%i)'
-    proc = Popen([sys.executable, '-c', command % (rep_port, sub_port)])
-
-    return proc, rep_port, sub_port
+    command = 'from IPython.zmq.kernel import main; main()'
+    proc = Popen([ sys.executable, '-c', command, 
+                   '--xrep', str(xrep_port), '--pub', str(pub_port) ])
+    return proc, xrep_port, pub_port
 
 
 if __name__ == '__main__':
-    base_port = 5575
-    main(rep_port = base_port, 
-         pub_port = base_port + 1)
+    main()

IPython/zmq/kernelmanager.py

@@ -6,6 +6,7 b' TODO: Create logger to handle debugging and console messages.'
 
 # Standard library imports.
 from Queue import Queue, Empty
+from subprocess import Popen
 from threading import Thread
 import time
 import traceback
@@ -18,8 +19,12 b' from zmq.eventloop import ioloop'
 # Local imports.
 from IPython.utils.traitlets import HasTraits, Any, Bool, Int, Instance, Str, \
     Type
+from kernel import launch_kernel
 from session import Session
 
+# Constants.
+LOCALHOST = '127.0.0.1'
+
 
 class MissingHandlerError(Exception):
     pass
@@ -49,19 +54,22 b' class ZmqSocketChannel(Thread):'
         Thread.__init__(self)
 
     def get_address(self):
-        """ Get the channel's address.
+        """ Get the channel's address. By the default, a channel is on 
+            localhost with no port specified (a negative port number).
         """
         return self._address
 
     def set_adresss(self, address):
         """ Set the channel's address. Should be a tuple of form:
-                (ip address [str], port [int])
-            or 'None' to indicate that no address has been specified.
+                (ip address [str], port [int]).
+            or None, in which case the address is reset to its default value.
         """
         # FIXME: Validate address.
         if self.is_alive():
             raise RuntimeError("Cannot set address on a running channel!")
         else:
+            if address is None:
+                address = (LOCALHOST, -1)
             self._address = address
 
     address = property(get_address, set_adresss)
@@ -314,6 +322,7 b' class KernelManager(HasTraits):'
     rep_channel_class = Type(RepSocketChannel)
     
     # Protected traits.
+    _kernel = Instance(Popen)
     _sub_channel = Any
     _xreq_channel = Any
     _rep_channel = Any
@@ -347,17 +356,26 b' class KernelManager(HasTraits):'
             self.rep_channel.stop()
 
     def start_kernel(self):
-        """Start a localhost kernel. If ports have been specified, use them.
-        Otherwise, choose an open port at random.
+        """Start a localhost kernel. If ports have been specified via the
+        address attributes, use them. Otherwise, choose open ports at random.
         """
-        # TODO: start a kernel.
-        self.start_listening()
+        xreq, sub = self.xreq_address, self.sub_address
+        if xreq[0] != LOCALHOST or sub[0] != LOCALHOST:
+            raise RuntimeError("Can only launch a kernel on localhost."
+                               "Make sure that the '*_address' attributes are "
+                               "configured properly.")
+
+        self._kernel, xrep, pub = launch_kernel(xrep_port=xreq[1], 
+                                                pub_port=sub[1])
+        self.xreq_address = (LOCALHOST, xrep)
+        self.sub_address = (LOCALHOST, pub)
 
     def kill_kernel(self):
-        """Kill the running kernel.
+        """Kill the running kernel, if there is one.
         """
-        # TODO: kill the kernel.
-        self.stop_listening()
+        if self._kernel:
+            self._kernel.kill()
+            self._kernel = None
 
     @property
     def is_alive(self):