Clarify event loop support in Term/Kernel

docs/source/config/eventloops.rst

@@ -1,103 +1,108 b''
 ================================
 Integrating with GUI event loops
 ================================
 
 When the user types ``%gui qt``, IPython integrates itself with the Qt event
 loop, so you can use both a GUI and an interactive prompt together. IPython
 supports a number of common GUI toolkits, but from IPython 3.0, it is possible
 to integrate other event loops without modifying IPython itself.
 
 Supported event loops include ``qt4``, ``qt5``, ``gtk2``, ``gtk3``, ``wx``,
 ``osx`` and ``tk``. Make sure the event loop you specify matches the GUI
 toolkit used by your own code.
 
 To make IPython GUI event loop integration occur automatically at every
 startup, set the ``c.InteractiveShellApp.gui`` configuration key in your
 IPython profile (see :ref:`setting_config`).
 
-Terminal IPython handles event loops very differently from the IPython kernel,
-so different steps are needed to integrate with each.
+If the event loop you use is supported by IPython, turning on event loop
+integration follows the steps just described whether you use Terminal IPython
+or an IPython kernel.
 
-Event loops in the terminal
----------------------------
+However, the way Terminal IPython handles event loops is very different from
+the way IPython kernel does, so if you need to integrate with a new kind of
+event loop, different steps are needed to integrate with each.
+
+Integrating with a new event loop in the terminal
+-------------------------------------------------
 
 .. versionchanged:: 5.0
 
    There is a new API for event loop integration using prompt_toolkit.
 
 In the terminal, IPython uses prompt_toolkit to prompt the user for input.
 prompt_toolkit provides hooks to integrate with an external event loop.
 
 To integrate an event loop, define a function which runs the GUI event loop
 until there is input waiting for prompt_toolkit to process. There are two ways
 to detect this condition::
 
     # Polling for input.
     def inputhook(context):
         while not context.input_is_ready():
             # Replace this with the appropriate call for the event loop:
             iterate_loop_once()
 
     # Using a file descriptor to notify the event loop to stop.
     def inputhook2(context):
         fd = context.fileno()
         # Replace the functions below with those for the event loop.
         add_file_reader(fd, callback=stop_the_loop)
         run_the_loop()
 
 Once you have defined this function, register it with IPython:
 
 .. currentmodule:: IPython.terminal.pt_inputhooks
 
 .. function:: register(name, inputhook)
 
    Register the function *inputhook* as the event loop integration for the
    GUI *name*. If ``name='foo'``, then the user can enable this integration
    by running ``%gui foo``.
 
 
-Event loops in the kernel
--------------------------
+Integrating with a new event loop in the kernel
+-----------------------------------------------
 
 The kernel runs its own event loop, so it's simpler to integrate with others.
 IPython allows the other event loop to take control, but it must call
 :meth:`IPython.kernel.zmq.kernelbase.Kernel.do_one_iteration` periodically.
 
 To integrate with this, write a function that takes a single argument,
 the IPython kernel instance, arranges for your event loop to call
 ``kernel.do_one_iteration()`` at least every ``kernel._poll_interval`` seconds,
 and starts the event loop.
 
 Decorate this function with :func:`IPython.kernel.zmq.eventloops.register_integration`,
 passing in the names you wish to register it for. Here is a slightly simplified
 version of the Tkinter integration already included in IPython::
 
     @register_integration('tk')
     def loop_tk(kernel):
         """Start a kernel with the Tk event loop."""
         from tkinter import Tk
 
         # Tk uses milliseconds
         poll_interval = int(1000*kernel._poll_interval)
         # For Tkinter, we create a Tk object and call its withdraw method.
         class Timer(object):
             def __init__(self, func):
                 self.app = Tk()
                 self.app.withdraw()
                 self.func = func
 
             def on_timer(self):
                 self.func()
                 self.app.after(poll_interval, self.on_timer)
 
             def start(self):
                 self.on_timer()  # Call it once to get things going.
                 self.app.mainloop()
 
         kernel.timer = Timer(kernel.do_one_iteration)
         kernel.timer.start()
 
 Some event loops can go one better, and integrate checking for messages on the
 kernel's ZMQ sockets, making the kernel more responsive than plain polling. How
 to do this is outside the scope of this document; if you are interested, look at
 the integration with Qt in :mod:`IPython.kernel.zmq.eventloops`.