--- a/PythonForJsProgrammers.txt	Tue Jun 10 23:49:06 2008 -0700
+++ b/PythonForJsProgrammers.txt	Tue Jun 10 23:52:50 2008 -0700
@@ -488,6 +488,18 @@
     >>> "Hello %(name)s, I need %(money)d dollars." % d
     'Hello bob, I need 5 dollars.'
 
+Keys for dictionaries can actually be any immutable type; this means
+that, for instance, tuples can be used as keys:
+
+    >>> a = {(1,2) : 1}
+
+But lists can't:
+
+    >>> b = {[1,2] : 1}
+    Traceback (most recent call last):
+    ...
+    TypeError: list objects are unhashable
+
 Python dictionaries generally aren't used to create arbitrary objects
 like they are in Javascript; they don't have prototypes, nor do they
 have meta-methods.  Instead, classes are used to do that sort of