Support for creating GUI apps and starting event loops.
IPython’s GUI integration allows interative plotting and GUI usage in IPython
session. IPython has two different types of GUI integration:
- The terminal based IPython supports GUI event loops through Python’s
PyOS_InputHook. PyOS_InputHook is a hook that Python calls periodically
whenever raw_input is waiting for a user to type code. We implement GUI
support in the terminal by setting PyOS_InputHook to a function that
iterates the event loop for a short while. It is important to note that
in this situation, the real GUI event loop is NOT run in the normal
manner, so you can’t use the normal means to detect that it is running.
- In the two process IPython kernel/frontend, the GUI event loop is run in
the kernel. In this case, the event loop is run in the normal manner by
calling the function or method of the GUI toolkit that starts the event
In addition to starting the GUI event loops in one of these two ways, IPython
will always create an appropriate GUI application object when GUi
integration is enabled.
If you want your GUI apps to run in IPython you need to do two things:
- Test to see if there is already an existing main application object. If
there is, you should use it. If there is not an existing application object
you should create one.
- Test to see if the GUI event loop is running. If it is, you should not
start it. If the event loop is not running you may start it.
This module contains functions for each toolkit that perform these things
in a consistent manner. Because of how PyOS_InputHook runs the event loop
you cannot detect if the event loop is running using the traditional calls
(such as wx.GetApp.IsMainLoopRunning() in wxPython). If PyOS_InputHook is
set These methods will return a false negative. That is, they will say the
event loop is not running, when is actually is. To work around this limitation
we proposed the following informal protocol:
- Whenever someone starts the event loop, they must set the _in_event_loop
attribute of the main application object to True. This should be done
regardless of how the event loop is actually run.
- Whenever someone stops the event loop, they must set the _in_event_loop
attribute of the main application object to False.
- If you want to see if the event loop is running, you must use hasattr
to see if _in_event_loop attribute has been set. If it is set, you
must use its value. If it has not been set, you can query the toolkit
in the normal manner.
- If you want GUI support and no one else has created an application or
started the event loop you must do this. We don’t want projects to
attempt to defer these things to someone else if they themselves need it.
The functions below implement this logic for each GUI toolkit. If you need
to create custom application subclasses, you will likely have to modify this
code for your own purposes. This code can be copied into your own project
so you don’t have to depend on IPython.