import Tkinter, fileinput, tkFileDialog

main_window=Tkinter.Tk()

text=Tkinter.Text(main_window,width=40,height=15,font="12")
text.pack()

of=tkFileDialog.askopenfile()


for i in fileinput.input(of):
    text.insert(Tkinter.END,i)

main_window.mainloop()

pydev debugger: starting
Traceback (most recent call last):
  File "D:\Setup\eclipse-SDK-3.7.1-win32\eclipse\plugins\org.python.pydev.debug_2.4.0.2012020116\pysrc\pydevd.py", line 1307, in <module>
    debugger.run(setup['file'], None, None)
  File "D:\Setup\eclipse-SDK-3.7.1-win32\eclipse\plugins\org.python.pydev.debug_2.4.0.2012020116\pysrc\pydevd.py", line 1060, in run
    pydev_imports.execfile(file, globals, locals) #execute the script
  File "D:\&#65533;&#65533;&#65533;&#65533;&#65533;&#65533;\&#65533;&#65533;&#65533; &#65533;&#65533;&#65533;&#65533;&#65533;&#65533;&#65533;&#65533;&#65533;\workspace\test_project\src\test_project.py", line 48, in <module>
    for i in fileinput.input(of):
  File "C:\Python27\lib\fileinput.py", line 253, in next
    line = self.readline()
  File "C:\Python27\lib\fileinput.py", line 345, in readline
    self._file = open(self._filename, self._mode)
IOError: [Errno 22] invalid mode ('r') or filename: '1231231231\n'

 print of

 <open file u'D:/Documents/Desktop/2.txt', mode 'r' at 0x02B75F40>