use pyzmq tools where appropriate

[minrk]

ZMQStream is the right object to use for event-driven handling of messages, but instead we had a duplication of half of it in KernelManager.

This removes most of the duplicate code, in favor of using ZMQStream.

also use the pyzmq install() function for using the pyzmq eventloop with tornado, instead of copying its contents into notebookapp.

[fperez]

Mmh, with this I can't start the notebook at all. Does it mean it changes the minimum tornado version required?

longs[junk]> ipnb
Traceback (most recent call last):
  File "/home/fperez/usr/bin/ipython", line 7, in <module>
    launch_new_instance()
  File "/home/fperez/usr/lib/python2.6/site-packages/IPython/frontend/terminal/ipapp.py", line 392, in launch_new_instance
    app.initialize()
  File "<string>", line 2, in initialize
  File "/home/fperez/usr/lib/python2.6/site-packages/IPython/config/application.py", line 84, in catch_config_error
    return method(app, *args, **kwargs)
  File "/home/fperez/usr/lib/python2.6/site-packages/IPython/frontend/terminal/ipapp.py", line 292, in initialize
    super(TerminalIPythonApp, self).initialize(argv)
  File "<string>", line 2, in initialize
  File "/home/fperez/usr/lib/python2.6/site-packages/IPython/config/application.py", line 84, in catch_config_error
    return method(app, *args, **kwargs)
  File "/home/fperez/usr/lib/python2.6/site-packages/IPython/core/application.py", line 325, in initialize
    self.parse_command_line(argv)
  File "/home/fperez/usr/lib/python2.6/site-packages/IPython/frontend/terminal/ipapp.py", line 287, in parse_command_line
    return super(TerminalIPythonApp, self).parse_command_line(argv)
  File "<string>", line 2, in parse_command_line
  File "/home/fperez/usr/lib/python2.6/site-packages/IPython/config/application.py", line 84, in catch_config_error
    return method(app, *args, **kwargs)
  File "/home/fperez/usr/lib/python2.6/site-packages/IPython/config/application.py", line 413, in parse_command_line
    return self.initialize_subcommand(subc, subargv)
  File "<string>", line 2, in initialize_subcommand
  File "/home/fperez/usr/lib/python2.6/site-packages/IPython/config/application.py", line 84, in catch_config_error
    return method(app, *args, **kwargs)
  File "/home/fperez/usr/lib/python2.6/site-packages/IPython/config/application.py", line 349, in initialize_subcommand
    subapp = import_item(subapp)
  File "/home/fperez/usr/lib/python2.6/site-packages/IPython/utils/importstring.py", line 40, in import_item
    module = __import__(package,fromlist=[obj])
  File "/home/fperez/usr/lib/python2.6/site-packages/IPython/frontend/html/notebook/notebookapp.py", line 35, in <module>
    ioloop.install()
AttributeError: 'module' object has no attribute 'install'

[minrk]

Sorry, the install() function is new in pyzmq-2.1.7 (from May), so I presume yours is older than that. We currently depend on 2.1.4 (except on Windows), so it should now fallback if it isn't defined.

The parallel code on Windows already depends on fixes in pyzmq-2.1.7, so we could consider updating the baseline.

[fperez]

I'd suggest not forcing unix users to update to > 2.1.4 if we don't really need it (in my case I can do it easily, but someone could be in a situation where they have for some reason a harder time), but emitting a warning if you have to use the fallback. That way we prod people to upgrade to avoid the warning. What do you think of that approach?

[minrk]

Since it's just this one function that we need, which is literally two lines of code, I'd leave out the warning. There are very few changes of any significance to people not using pyzmq directly, after 2.1.4. Most of the changes to pyzmq since then are user-level sugar, or related to libzmq-3.x compatibility.

[fperez]

Got it. In that case, merging now. I tested it and everything seemed OK, the code looks clean, and I'm glad to see this kind of cleanup. Thanks!