Tkinter grid_info()

Please could someone tell me why this is not working?

from Tkinter import *

root = Tk()
e = Entry(root)
e.grid(column=0, row=0)
info = e.grid_info()
print "row:", info["row"], "column:", info["column"]
root.mainloop()

Running this displays the following error:

Traceback (most recent call last):
  File "test.py", line 6, in <module>
    grid_info = e.grid_info()
  File "/usr/lib/python2.7/lib-tk/Tkinter.py", line 2000, in grid_info
    self.tk.call('grid', 'info', self._w))
TypeError: coercing to Unicode: need string or buffer, _tkinter.Tcl_Obj
found