scroll bar

why this code is no giving any scroll?

re: scroll bar

forgot the code, sorry,
the code:
import wx

class MyFrame(wx.Frame):
def __init__(self, parent, ID, title):
wx.Frame.__init__(self, parent, ID, title, size=(400, 250))

myscrolledwindow = wx.PyScrolledWindow(self, -1)
sizer = wx.BoxSizer()
myscrolledwindow.SetSizer(sizer)
myscrolledwindow.SetScrollRate(1,1)


app = wx.PySimpleApp()
frame = MyFrame(None, -1, "Sizer Test")
frame.Show()
app.MainLoop()