[WxPython] TypeError: request for something already fulfilled?

[merlem]

One case more in these things...

import wx

gridcontent = [["1", "2", "3", "4"],
               ["5", "6", "7", "8"]]

class Mainframe(wx.Frame):
    def __init__(self, parent, id, title):
        wx.Frame.__init__(self, parent, id, title)

        self.grid = wx.GridBagSizer()
        for rownum, gridcontentrow in enumerate(gridcontent):
            for colnum, string in enumerate(gridcontentrow):
                pos = (rownum, colnum)
                print pos
                self.grid.Add(string, pos)
                
        self.SetSizer(self.grid)
        
if __name__ == "__main__": 

    app = wx.App(0)
    preframe = Mainframe(None, -1, "Datenanzeige")   
    app.MainLoop() 

gives

Error:
Traceback (most recent call last):
  File "...Gridbagsizerpos01a.py", line 20, in <module>
    preframe = Mainframe(None, -1, "Datenanzeige")
  File "...Gridbagsizerpos01a.py", line 15, in __init__
    self.grid.Add(string, pos)
  File "...Python27\lib\site-packages\wx-2.8-msw-unicode\wx\_core.py", line 14086, in Add
    return _core_.GridBagSizer_Add(*args, **kwargs)
TypeError: wx.Window, wx.Sizer, wx.Size, or (w,h) expected for item

The wxpython docs claim: "wxPython has typemaps that will automatically convert from a 2-element sequence of integers to a wx.GBPosition, so you can use the more pythonic representation of the position nearly transparently in Python code."
Then why does (0, 0) not fullfill the requirements of (w,h) or the requirement of being a position respectively, as is needed by GridBagSizer.Add(self, item, pos, span=DefaultSpan, flag=0, border=0, userData=None)?