From de5aff1bdc65a562c15cdd5a661dc666cb25ec16 Mon Sep 17 00:00:00 2001 From: Georg Brandl Date: Sun, 6 Oct 2013 10:22:45 +0200 Subject: [PATCH] Closes #18646: improve lambda docs in tutorial. Original patch by Terry Reedy. --- Doc/tutorial/controlflow.rst | 27 +++++++++++++++++---------- 1 file changed, 17 insertions(+), 10 deletions(-) diff --git a/Doc/tutorial/controlflow.rst b/Doc/tutorial/controlflow.rst index 055f547241e..56df73dc470 100644 --- a/Doc/tutorial/controlflow.rst +++ b/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 -languages like Lisp have been added to Python. With the :keyword:`lambda` -keyword, small anonymous functions can be created. Here's a function that -returns the sum of its two arguments: ``lambda a, b: a+b``. Lambda forms can be -used wherever function objects are required. They are syntactically restricted -to a single expression. Semantically, they are just syntactic sugar for a -normal function definition. Like nested function definitions, lambda forms can -reference variables from the containing scope:: +Small anonymous functions can be created with the :keyword:`lambda` keyword. +This function returns the sum of its two arguments: ``lambda a, b: a+b``. +Lambda forms can be used wherever function objects are required. They are +syntactically restricted to a single expression. Semantically, they are just +syntactic sugar for a normal function definition. Like nested function +definitions, lambda functions can 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: