# App Overview¶

## Introduction¶

A wxPython application does not have a main procedure; the equivalent is the wx.AppConsole.OnInit member defined for a class derived from wx.App.

OnInit will usually create a top window as a bare minimum. Unlike in earlier versions of wxPython, OnInit does not return a frame. Instead it returns a boolean value which indicates whether processing should continue (True) or not (False).

An application closes by destroying all windows. Because all frames must be destroyed for the application to exit, it is advisable to use parent frames wherever possible when creating new frames, so that deleting the top level frame will automatically delete child frames. The alternative is to explicitly delete child frames in the top-level frame’s wx.CloseEvent handler.

In emergencies the wx.Exit function can be called to kill the application however, normally the application shuts down automatically when the last top-level window closes. See Application Shutdown.

An example of defining an application follows:

class DerivedApp(wx.App):

def OnInit(self):
the_frame = wx.Frame(None, -1)

# Other initialization code...
the_frame.Show(True)
return True


## Application Shutdown¶

The application normally shuts down when the last of its top level windows is closed. This is normally the expected behaviour and means that it is enough to call wx.Window.Close in response to the “Exit” menu command if your program has a single top level window. If this behavior is not desirable wx.PyApp.SetExitOnFrameDelete can be called to change it.

Note

Note that such logic doesn’t apply for the windows shown before the program enters the main loop: in other words, you can safely show a dialog from wx.AppConsole.OnInit and not be afraid that your application terminates when this dialog – which is the last top level window for the moment – is closed.

Another aspect of the application shutdown is wx.AppConsole.OnExit which is called when the application exits but before wxPython cleans up its internal structures.