Calcolatrice con interfaccia grafica in Python

import wx

class MyFrame3(wx.Frame):
    def __init__(self, *args, **kwds):
        kwds["style"] = wx.DEFAULT_FRAME_STYLE
        wx.Frame.__init__(self, *args, **kwds)
        self.cls = wx.Button(self, -1, "Cancella")
        self.back = wx.Button(self, -1, "Indietro")
        self.close = wx.Button(self, -1, "Chiudi")
        self.seven = wx.Button(self, -1, "7")
        self.eight = wx.Button(self, -1, "8")
        self.nine = wx.Button(self, -1, "9")
        self.divide = wx.Button(self, -1, "/")
        self.four = wx.Button(self, -1, "4")
        self.five = wx.Button(self, -1, "5")
        self.six = wx.Button(self, -1, "6")
        self.multiply = wx.Button(self, -1, "*")
        self.one = wx.Button(self, -1, "1")
        self.two = wx.Button(self, -1, "2")
        self.three = wx.Button(self, -1, "3")
        self.minus = wx.Button(self, -1, "-")
        self.zero = wx.Button(self, -1, "0")
        self.dot = wx.Button(self, -1, ".")
        self.equal = wx.Button(self, -1, "=")
        self.plus = wx.Button(self, -1, "+")

        self.frame_3_menubar = wx.MenuBar()
        self.files = wx.Menu()
        self.Quit = wx.MenuItem(self.files, 130, "ChiuditAlt+F4", "", wx.ITEM_NORMAL)
    self.Quit.SetBitmap(wx.Bitmap('icons/Exit.png'))
    self.files.AppendItem(self.Quit)
        self.frame_3_menubar.Append(self.files, "File")
        self.SetMenuBar(self.frame_3_menubar)

        self.__set_properties()
        self.__do_layout()
    self.formula = False

    self.Bind(wx.EVT_BUTTON, self.OnCls, self.cls)
        self.Bind(wx.EVT_BUTTON, self.OnBack, self.back)
        self.Bind(wx.EVT_BUTTON, self.OnClose, self.close)
        self.Bind(wx.EVT_BUTTON, self.OnSeven, self.seven)
        self.Bind(wx.EVT_BUTTON, self.OnEight, self.eight)
        self.Bind(wx.EVT_BUTTON, self.OnNine, self.nine)
        self.Bind(wx.EVT_BUTTON, self.OnDivide, self.divide)
        self.Bind(wx.EVT_BUTTON, self.OnFour, self.four)
        self.Bind(wx.EVT_BUTTON, self.OnFive, self.five)
        self.Bind(wx.EVT_BUTTON, self.OnSix, self.six)
        self.Bind(wx.EVT_BUTTON, self.OnMultiply, self.multiply)
        self.Bind(wx.EVT_BUTTON, self.OnOne, self.one)
        self.Bind(wx.EVT_BUTTON, self.OnTwo, self.two)
        self.Bind(wx.EVT_BUTTON, self.OnThree, self.three)
        self.Bind(wx.EVT_BUTTON, self.OnMinus, self.minus)
        self.Bind(wx.EVT_BUTTON, self.OnZero, self.zero)
        self.Bind(wx.EVT_BUTTON, self.OnDot, self.dot)
        self.Bind(wx.EVT_BUTTON, self.OnEqual, self.equal)
        self.Bind(wx.EVT_BUTTON, self.OnPlus, self.plus)
        self.Bind(wx.EVT_MENU, self.Onquit, self.Quit)

    def __set_properties(self):
        self.SetTitle("ShinWorld Calculator")
    _icon = wx.EmptyIcon()
        _icon.CopyFromBitmap(wx.Bitmap("icons/OD.ico", wx.BITMAP_TYPE_ANY))
        self.SetIcon(_icon)

    def __do_layout(self):
        sizer_1 = wx.BoxSizer(wx.VERTICAL)
    self.display = wx.TextCtrl(self, -1, '',  style=wx.TE_RIGHT)
    sizer_1.Add(self.display, 0, wx.EXPAND | wx.TOP | wx.BOTTOM, 4)
        grid_sizer_1 = wx.GridSizer(4, 4, 3, 3)
        grid_sizer_1.Add(self.cls, 0, wx.EXPAND, 6)
        grid_sizer_1.Add(self.back, 0, wx.EXPAND, 6)
    grid_sizer_1.Add(wx.StaticText(self, -1, ''), 0, wx.EXPAND),
        grid_sizer_1.Add(self.close, 0, wx.EXPAND, 0)
        grid_sizer_1.Add(self.seven, 0, wx.EXPAND, 0)
        grid_sizer_1.Add(self.eight, 0, wx.EXPAND, 0)
        grid_sizer_1.Add(self.nine, 0, wx.EXPAND, 0)
        grid_sizer_1.Add(self.divide, 0, wx.EXPAND, 0)
        grid_sizer_1.Add(self.four, 0, wx.EXPAND, 0)
        grid_sizer_1.Add(self.five, 0, wx.EXPAND, 0)
        grid_sizer_1.Add(self.six, 0, wx.EXPAND, 0)
        grid_sizer_1.Add(self.multiply, 0, wx.EXPAND, 0)
        grid_sizer_1.Add(self.one, 0, wx.EXPAND, 0)
        grid_sizer_1.Add(self.two, 0, wx.EXPAND, 0)
        grid_sizer_1.Add(self.three, 0, wx.EXPAND, 0)
        grid_sizer_1.Add(self.minus, 0, wx.EXPAND, 0)
        grid_sizer_1.Add(self.zero, 0, wx.EXPAND, 0)
        grid_sizer_1.Add(self.dot, 0, wx.EXPAND, 0)
        grid_sizer_1.Add(self.equal, 0, wx.EXPAND, 0)
        grid_sizer_1.Add(self.plus, 0, wx.EXPAND, 0)
        sizer_1.Add(grid_sizer_1, 4, wx.EXPAND|wx.ALIGN_BOTTOM, 0)
        self.SetSizer(sizer_1)
        sizer_1.Fit(self)
        self.Layout()
        self.Centre()

    def OnCls(self, event):
    self.display.Clear()

    def OnBack(self, event):
    formula = self.display.GetValue()
    self.display.Clear()
    self.display.SetValue(formula[:-1])

    def OnClose(self, event):
    self.Close()

    def OnSeven(self, event):
    if self.formula:
        self.display.Clear()
        self.formula = False
    self.display.AppendText('7')

    def OnEight(self, event):
    if self.formula:
        self.display.Clear()
        self.formula = False
    self.display.AppendText('8')

    def OnNine(self, event):
    if self.formula:
        self.display.Clear()
        self.formula = False
    self.display.AppendText('9')

    def OnDivide(self, event):
        if self.formula:
        return
    self.display.AppendText('/')

    def OnFour(self, event):
    if self.formula:
        self.display.Clear()
        self.formula = False
    self.display.AppendText('4')

    def OnFive(self, event):
    if self.formula:
        self.display.Clear()
        self.formula = False
    self.display.AppendText('5')

    def OnSix(self, event):
    if self.formula:
        self.display.Clear()
        self.formula = False
    self.display.AppendText('6')

    def OnMultiply(self, event):
        if self.formula:
        return
    self.display.AppendText('*')

    def OnOne(self, event):
    if self.formula:
        self.display.Clear()
        self.formula = False
    self.display.AppendText('1')

    def OnTwo(self, event):
    if self.formula:
        self.display.Clear()
        self.formula = False
    self.display.AppendText('2')

    def OnThree(self, event):
    if self.formula:
        self.display.Clear()
        self.formula = False
    self.display.AppendText('3')

    def OnMinus(self, event):
        if self.formula:
        return
    self.display.AppendText('-')

    def OnZero(self, event):
    if self.formula:
        self.display.Clear()
        self.formula = False
    self.display.AppendText('0')

    def OnDot(self, event):
        if self.formula:
        return
    self.display.AppendText('.')

    def OnEqual(self, event):
        if self.formula:
            return
        formula = self.display.GetValue()
        self.formula = False
        try:
        self.display.Clear()
        output = eval(formula)
        self.display.AppendText(str(output))
    except StandardError:
        dlg = wx.MessageDialog(self, 'Errore durante l'esecuzione!', 'ShinWorld Calculetor', wx.OK | wx.ICON_ERROR)
        dlg.ShowModal()
        dlg.Destroy()

    def OnPlus(self, event):
        if self.formula:
        return
    self.display.AppendText('+')

    def Onquit(self, event):
    self.Close()

class MyApp3(wx.App):
    def OnInit(self):
        wx.InitAllImageHandlers()
        frame_3 = MyFrame3(None, -1, "")
        self.SetTopWindow(frame_3)
        frame_3.Show()
        return 1

if __name__ == "__main__":
    app3 = MyApp3(0)
    app3.MainLoop()