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# Module: `lib.guisupport`

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:

1. 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.
2. 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 loop.

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:

1. 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.
2. 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.

## 6 Functions

`IPython.lib.guisupport.``get_app_wx`(*args, **kwargs)

  Create a new wx app or return an exiting one.

`IPython.lib.guisupport.``is_event_loop_running_wx`(app=None)

  Is the wx event loop running.

`IPython.lib.guisupport.``start_event_loop_wx`(app=None)

  Start the wx event loop in a consistent manner.

`IPython.lib.guisupport.``get_app_qt4`(*args, **kwargs)

  Create a new qt4 app or return an existing one.

`IPython.lib.guisupport.``is_event_loop_running_qt4`(app=None)

  Is the qt4 event loop running.

`IPython.lib.guisupport.``start_event_loop_qt4`(app=None)

  Start the qt4 event loop in a consistent manner.

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