import wx

class MyApp(wx.App):

    def OnInit(self):
        frame = wx.Frame(None, -1, f_label)
        self.n_pressed = 0
        label = "Hello! (%d)" %(self.n_pressed)
        self.button = wx.Button(frame, -1, label)
        self.button.Bind(wx.EVT_BUTTON, self.myButtonHandler)
        self.SetTopWindow(frame)
        self.frame.Show(True)
        return True

    def myButtonHandler(self, evt):
        self.n_pressed += 1
        label = "Hello! (%d)" %(self.n_pressed)
        self.button.SetLabel(label)

app = MyApp(0)
app.MainLoop()