I've implemented iterkeys(), itervalues() and iteritems() methods for

dictionaries.  These do away with the myth that iterating over the
keys and extracting the values is as fast as iterating over the items;
it is about 7% slower.

pep-0234.txt

@@ -166,6 +166,18 @@ Dictionary Iterators
       as long as the restriction on modifications to the dictionary
       (either by the loop or by another thread) are not violated.
 
+    - Add methods to dictionaries that return different kinds of
+      iterators explicitly:
+
+          for key in dict.iterkeys(): ...
+
+          for value in dict.itervalues(): ...
+
+          for key, value in dict.iteritems(): ...
+
+      This means that "for x in dict" is shorthand for "for x in
+      dict.iterkeys()".
+
     If this proposal is accepted, it makes sense to recommend that
     other mappings, if they support iterators at all, should also
     iterate over the keys.  However, this should not be taken as an
@@ -299,24 +311,18 @@ Open Issues
       this is true, I (Guido) find the correspondence between "for x in
       dict" and "if x in dict" too compelling to break, and there's not
       much overhead in having to write dict[x] to explicitly get the
-      value.  I've also timed the difference between
+      value.
+
+      For fast iteration over items, use "for key, value in
+      dict.iteritems()".  I've timed the difference between
 
           for key in dict: dict[key]
 
       and
 
-          for key, value in dict[key]: pass
+          for key, value in dict.iteritems(): pass
 
-      and found that these run at about the same speed.
+      and found that the latter is only about 7% faster.
-
-      We could also add methods to dictionaries that return different
-      kinds of iterators, e.g.
-
-          for key, value in dict.iteritems(): ...
-
-          for value in dict.itervalues(): ...
-
-          for key in dict.iterkeys(): ...
 
 
 Resolved Issues