While investigating for the stdlib reorg of Tkinter, I came across the
following error:

~/dev/py3k$ ./python Lib/lib-tk/Dialog.py 
Traceback (most recent call last):
  File "Lib/lib-tk/Dialog.py", line 45, in <module>
    Pack: {}})
  File "/home/quentin/dev/py3k/Lib/lib-tk/Tkinter.py", line 1996, in
__init__
    Widget.__init__(self, master, 'button', cnf, kw)
  File "/home/quentin/dev/py3k/Lib/lib-tk/Tkinter.py", line 1921, in
__init__
    for k in cnf.keys():
RuntimeError: dictionary changed size during iteration


The attached patch adds list() around the dict.keys() call.

On a related note, this doesn't appear to be an isolated error, since a
similar issue (#1649) was recently fixed in r59554. Would it be a good
idea to look for other identical cases ?