merge with 3.3

Doc/tutorial/controlflow.rst

@@ -583,17 +583,16 @@ In the same fashion, dictionaries can deliver keyword arguments with the ``**``\
 
 .. _tut-lambda:
 
-Lambda Forms
+Lambda Expressions
-------------
+------------------
 
-By popular demand, a few features commonly found in functional programming
+Small anonymous functions can be created with the :keyword:`lambda` keyword.
-languages like Lisp have been added to Python.  With the :keyword:`lambda`
+This function returns the sum of its two arguments: ``lambda a, b: a+b``.
-keyword, small anonymous functions can be created. Here's a function that
+Lambda forms can be used wherever function objects are required.  They are
-returns the sum of its two arguments: ``lambda a, b: a+b``.  Lambda forms can be
+syntactically restricted to a single expression.  Semantically, they are just
-used wherever function objects are required.  They are syntactically restricted
+syntactic sugar for a normal function definition.  Like nested function
-to a single expression.  Semantically, they are just syntactic sugar for a
+definitions, lambda functions can reference variables from the containing
-normal function definition.  Like nested function definitions, lambda forms can
+scope::
-reference variables from the containing scope::
 
    >>> def make_incrementor(n):
    ...     return lambda x: x + n
@@ -604,6 +603,14 @@ reference variables from the containing scope::
    >>> f(1)
    43
 
+The above example uses a lambda expression to return a function.  Another use
+is to pass a small function as an argument::
+
+   >>> pairs = [(1, 'one'), (2, 'two'), (3, 'three'), (4, 'four')]
+   >>> pairs.sort(key=lambda pair: pair[1])
+   >>> pairs
+   [(4, 'four'), (1, 'one'), (3, 'three'), (2, 'two')]
+
 
 .. _tut-docstrings: