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Interpreter error results in erroneous exception when running a script
under debugger control.
Full repro description:
On Windows System, try to run idle.py under the inspection of pdb.py. 
Note that you must set a breakpoint somewhere otherwise pdb will not
trace the script and the issue will not surface.
You should get the bad exception in line 295 of multicall.py
Python complains that a local variable has been used before being
declared while in effect it has been a couple of lines before that point.
Nir

For reference, here is the output of the pdb session:
gbr@lap ~/devel/python> ./python Lib/pdb.py Lib/idlelib/idle.py
> /home/gbr/devel/python/Lib/idlelib/idle.py(1)<module>()
-> try:
(Pdb) break multicall.py:300
*** 'multicall.py' not found from sys.path
(Pdb) break idle.py:10
Breakpoint 1 at /home/gbr/devel/python/Lib/idlelib/idle.py:10
(Pdb) c
Traceback (most recent call last):
 File "/home/gbr/devel/python/Lib/pdb.py", line 1275, in main
 pdb._runscript(mainpyfile)
 File "/home/gbr/devel/python/Lib/pdb.py", line 1192, in _runscript
 self.run(statement)
 File "/home/gbr/devel/python/Lib/bdb.py", line 366, in run
 exec cmd in globals, locals
 File "<string>", line 1, in <module>
 File "Lib/idlelib/idle.py", line 21, in <module>
 idlelib.PyShell.main()
 File "/home/gbr/devel/python/Lib/idlelib/PyShell.py", line 1396, in main
 shell = flist.open_shell()
 File "/home/gbr/devel/python/Lib/idlelib/PyShell.py", line 275, in
open_shell
 self.pyshell = PyShell(self)
 File "/home/gbr/devel/python/Lib/idlelib/PyShell.py", line 816, in
__init__
 OutputWindow.__init__(self, flist, None, None)
 File "/home/gbr/devel/python/Lib/idlelib/OutputWindow.py", line 16, in
__init__
 EditorWindow.__init__(self, *args)
 File "/home/gbr/devel/python/Lib/idlelib/EditorWindow.py", line 108,
in __init__
 self.text = text = MultiCallCreator(Text)(
 File "/home/gbr/devel/python/Lib/idlelib/MultiCall.py", line 294, in
MultiCallCreator
 class MultiCall (widget):
 File "/home/gbr/devel/python/Lib/idlelib/MultiCall.py", line 295, in
MultiCall
 assert issubclass(widget, Tkinter.Misc)
NameError: free variable 'widget' referenced before assignment in
enclosing scope
Uncaught exception. Entering post mortem debugging
Running 'cont' or 'step' will restart the program
> /home/gbr/devel/python/Lib/idlelib/MultiCall.py(295)MultiCall()
-> assert issubclass(widget, Tkinter.Misc)
(Pdb) 
I *think* we had some similar issue with trace functions and class
scopes in the past, but can't remember where.

This issue is a duplicate of issue2378; the patch attached there
corrects this problem. I will commit it tonight.