Peter Haight discovered that this code uses a mutable default for cnf

gvanrossum · gvanrossum · commit ea7364c7cd98 · 1999-09-20T00:39:47.000Z
and then (under certain circumstances) can clobber the default!
He also submitted this patch as PR#82.
diff --git a/Lib/lib-tk/ScrolledText.py b/Lib/lib-tk/ScrolledText.py
@@ -14,7 +14,9 @@
 from Tkinter import _cnfmerge
 
 class ScrolledText(Text):
-	def __init__(self, master=None, cnf={}, **kw):
+	def __init__(self, master=None, cnf=None, **kw):
+		if cnf is None:
+			cnf = {}
 		if kw:
 			cnf = _cnfmerge((cnf, kw))
 		fcnf = {}
