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In ScrolledCanvas.__init__() there's a name conflict with a methodname
of the parentclass Frame: _root. The bugfix consists in renaming this
attribute, which occurs only twice. No change in behaviour at all.
Regards,
Gregor

This patch applies to Python 2.6 as well
Gregor

I'd like to see this patch accepted and done for Python 2.6.1 and (at
the same time) python 3.0 before the last rc is released. So could you
dedicate a few minutes to reviewing it.
To demonstrate the nature of this issue (and also the nuisance it could
produce) I've constructed a minimal example to show the consequences of
the bug:
import turtle
s = turtle.Screen()
def changecolor():
 s.bgcolor(1.0, 0.5) # needs 3 floats as arguments
s.ontimer(changecolor, 1000)
turtle.mainloop()
This should create an error message like this:
....
TurtleGraphicsError: bad color arguments: (100, 100)
Instead it results in:
Traceback (most recent call last):
 File "C:\_\provoke_error.py", line 11, in <module>
 turtle.mainloop()
 File "C:\Python26\lib\lib-tk\Tkinter.py", line 325, in mainloop
 _default_root.tk.mainloop(n)
 File "C:\Python26\lib\lib-tk\Tkinter.py", line 1414, in __call__
 self.widget._report_exception()
 File "C:\Python26\lib\lib-tk\Tkinter.py", line 1175, in _report_exception
 root = self._root()
AttributeError: _Root instance has no __call__ method
because the _root() method defined in line 1105 of Tkinter.py is
overwritten by the _root attribute of ScrolledCanvas (lines 362 and
382). So in these (hopefully rare) cases where an error message is
directly provoked from the Tkinter module, this will fail letting the
user without clue about what happened. 
With the proposed patch applied, the above script produces the correct
error message.
Regards, Gregor

Thanks for the patch. Committed as r67279, r67280, and r67281.