SF patch #980695: efficient string concatenation

(Original patch by Armin Rigo).

pep-0008.txt

@@ -521,6 +521,15 @@ Naming Conventions
 
 Programming Recommendations
 
+    - Code should be written in a way that does not disadvantage other
+      implementations of Python (PyPy, Jython, IronPython, Pyrex, Psyco,
+      and such).  For example, do not rely on CPython's efficient
+      implementation of in-place string concatenation for statements in
+      the form a+=b or a=a+b.  Those statements run more slowly in
+      Jython.  In performance sensitive parts of the library, the
+      ''.join() form should be used instead.  This will assure that
+      concatenation occurs in linear time across various implementations.
+
     - Comparisons to singletons like None should always be done with
       'is' or 'is not'.  Also, beware of writing "if x" when you
       really mean "if x is not None" -- e.g. when testing whether a