Learning wxPython by Example.

The Full Example

The following code shows an example of a wxPython application with a frame containing a menu bar, status bar and panel. The panel contains a label and a button that is bound to an exit function. The menu bar has a Help->About action that is bound to a dialog box. The dialog box shows how to display an HTML message and bring up a link in the user's default browser. You might find this example useful as a starting point that you can adapt. In a larger program it would be best to put the about box code into a separate file so that the main program file does not become too large. If this example is too large to start with then see the second example.

# -*- coding: <<encoding>> -*-
#-------------------------------------------------------------------------------
#   <<project>>
# 
#-------------------------------------------------------------------------------

import wxversion
wxversion.select("2.8")
import wx, wx.html
import sys

aboutText = """<p>Sorry, there is no information about this program. It is
running on version %(wxpy)s of <b>wxPython</b> and %(python)s of <b>Python</b>.
See <a href="http://wiki.wxpython.org">wxPython Wiki</a></p>""" 

class HtmlWindow(wx.html.HtmlWindow):
    def __init__(self, parent, id, size=(600,400)):
        wx.html.HtmlWindow.__init__(self,parent, id, size=size)
        if "gtk2" in wx.PlatformInfo:
            self.SetStandardFonts()

    def OnLinkClicked(self, link):
        wx.LaunchDefaultBrowser(link.GetHref())
        
class AboutBox(wx.Dialog):
    def __init__(self):
        wx.Dialog.__init__(self, None, -1, "About <<project>>",
            style=wx.DEFAULT_DIALOG_STYLE|wx.THICK_FRAME|wx.RESIZE_BORDER|
                wx.TAB_TRAVERSAL)
        hwin = HtmlWindow(self, -1, size=(400,200))
        vers = {}
        vers["python"] = sys.version.split()[0]
        vers["wxpy"] = wx.VERSION_STRING
        hwin.SetPage(aboutText % vers)
        btn = hwin.FindWindowById(wx.ID_OK)
        irep = hwin.GetInternalRepresentation()
        hwin.SetSize((irep.GetWidth()+25, irep.GetHeight()+10))
        self.SetClientSize(hwin.GetSize())
        self.CentreOnParent(wx.BOTH)
        self.SetFocus()

class Frame(wx.Frame):
    def __init__(self, title):
        wx.Frame.__init__(self, None, title=title, pos=(150,150), size=(350,200))
        self.Bind(wx.EVT_CLOSE, self.OnClose)

        menuBar = wx.MenuBar()
        menu = wx.Menu()
        m_exit = menu.Append(wx.ID_EXIT, "E&xit\tAlt-X", "Close window and exit program.")
        self.Bind(wx.EVT_MENU, self.OnClose, m_exit)
        menuBar.Append(menu, "&File")
        menu = wx.Menu()
        m_about = menu.Append(wx.ID_ABOUT, "&About", "Information about this program")
        self.Bind(wx.EVT_MENU, self.OnAbout, m_about)
        menuBar.Append(menu, "&Help")
        self.SetMenuBar(menuBar)
        
        self.statusbar = self.CreateStatusBar()

        panel = wx.Panel(self)
        box = wx.BoxSizer(wx.VERTICAL)
        
        m_text = wx.StaticText(panel, -1, "Hello World!")
        m_text.SetFont(wx.Font(14, wx.SWISS, wx.NORMAL, wx.BOLD))
        m_text.SetSize(m_text.GetBestSize())
        box.Add(m_text, 0, wx.ALL, 10)
        
        m_close = wx.Button(panel, wx.ID_CLOSE, "Close")
        m_close.Bind(wx.EVT_BUTTON, self.OnClose)
        box.Add(m_close, 0, wx.ALL, 10)
        
        panel.SetSizer(box)
        panel.Layout()

    def OnClose(self, event):
        dlg = wx.MessageDialog(self, 
            "Do you really want to close this application?",
            "Confirm Exit", wx.OK|wx.CANCEL|wx.ICON_QUESTION)
        result = dlg.ShowModal()
        dlg.Destroy()
        if result == wx.ID_OK:
            self.Destroy()

    def OnAbout(self, event):
        dlg = AboutBox()
        dlg.ShowModal()
        dlg.Destroy()  

app = wx.App(redirect=True)   # Error messages go to popup window
top = Frame("<<project>>")
top.Show()
app.SetTopWindow(top)
app.MainLoop()

A Bare-Bones Example

The following is a minimum wxPython application in the tradition of Hello World:

import wx

app = wx.App(redirect=True)
top = wx.Frame(None, title="Hello World", size=(300,200))
top.Show()
app.SetTopWindow(top)
app.MainLoop()

• The first thing to do in the main program is to create the wx.App object that provides the event loop. You need to do this first because some other objects use it behind the scenes. The "redirect=True" option

• The topmost GUI interface element, or widget, is the wx.Frame. All it consists of is an empty rectangular frame with a title bar. In all but this very basic example the frame would be sub-classed to allow the definition of further widgets and call-back functions within it.

• The frame and its contents are not displayed automatically. You must explicitly call the Show() function.
• The application needs to know which is the main frame.
• At this point the application is visible on the screen but is not responding to events. You must call the Main Loop function to do this but note that once started the event loop never returns. Although no events have been defined explicitly there are some event handlers provided by wxPython. If you click on the X icon on the title bar the application receives a wx.EVT_CLOSE event that tells the application to terminate.

Sub-Classing the Frame

To develop this application further you need to add your own frame object before you can add functionality to the wx.Frame.

import wx

class Frame(wx.Frame):
    def __init__(self, title):
        wx.Frame.__init__(self, None, title=title, size=(350,200))

app = wx.App(redirect=True)
top = Frame("Hello World")
top.Show()
app.SetTopWindow(top)
app.MainLoop()

If you are not very familiar with using objects in Python you should look closely at this example as sub-classing is used quite frequently in wxPython. In this example the Frame class is based on wx.Frame. Any functions that appear in the derived class will hide those of the same name in the base class. This commonly applies to the init function that is called automatically when a new object is defined. In this case the statement is "top = Frame("Hello World"). It is necessary for the derived class to call the init function in the base class explicitly. Note that the first argument is "self" so that the base class knows what object is being initialized.

Adding an Event Handler

class Frame(wx.Frame):
    def __init__(self, title):
        wx.Frame.__init__(self, None, title=title, size=(350,200))
        self.Bind(wx.EVT_CLOSE, self.OnClose)

    def OnClose(self, event):
        dlg = wx.MessageDialog(self, 
            "Do you really want to close this application?",
            "Confirm Exit", wx.OK|wx.CANCEL|wx.ICON_QUESTION)
        result = dlg.ShowModal()
        dlg.Destroy()
        if result == wx.ID_OK:
            self.Destroy()

This example shows how to add a function that will handle the wx.EVT_CLOSE event that is generated when the user clicks on the X icon on the title bar of the frame. The Bind function tells the event loop the name of the function to call when the event is detected. It is a useful convention to start the name of any event handlers with "On". This helps to ensure that the function name does not clash with one in the base class.

The On Close function illustrates how to use a message dialog. The ShowModal function not only displays the dialog but also waits for the user to click on one of the buttons. The result is either wx.ID_OK or wx.ID_CANCEL. The Destroy function is used to terminate the application when the OK button is pressed. If "self.Close()" had been used instead of "self.Destroy()" the program would get into a loop as a further wx.EVT_CLOSE event would be issued.

The full example is based on the wxPython template that is used in the Luke-SDK IDE.