Broken code for drawing BG on wxPanel

import wx
import random
import os, sys
import traceback

class BlahFrame(wx.Frame):
    def __init__(self, parent, id, size):
        wx.Frame.__init__(self, parent, id, "Hello world!", size)

        # Create panel
        self.panel = wx.Panel(self)

        # Background setup
        if sys.platform == "linux22":
            print "wxGTK? YUCK!"
        else:
            print "Loading image from: "+os.path.join(os.getcwd(), "stripebg.png")
            self.bmp1 = wx.Bitmap(os.path.join(os.getcwd(), "stripebg.png"))
            self.Bind(wx.EVT_PAINT, self.on_paint)
            self.Bind(wx.EVT_SIZE, self.on_size)
        self.SetSize(size)
        self.invalidated = True
        self.button1 = wx.Button(self.panel, -1, label='Button1', pos=(10, 5))
        self.Show()

    def on_paint(self, event):
        # Draw BG of panel
        dc = wx.PaintDC(self.panel)
        w, h = dc.GetSize()
        # get image width and height
        iw = self.bmp1.GetWidth()
        ih = self.bmp1.GetHeight()
        for x in range(0, self.panel.GetSize()[0], iw):
            for y in range(0, self.panel.GetSize()[1], ih):
                dc.DrawBitmap(self.bmp1, x, y, True)
app = wx.PySimpleApp()

try:
    BlahInstance = BlahFrame(None, -1, size=(700,800))
    app.SetTopWindow(BlahInstance)
    app.MainLoop()
except:
    print "Crashed..."
    traceback.print_exc()