Python学习笔记：循环技巧

本篇参考官方文档： The PythonTutorial 5.6Looping Techniques

当循环一个序列（sequence）的时候，位置索引和相应的值可以一起检索，用 enumerate()函数。

>>> for i, v in enumerate(['tic', 'tac', 'toe']):...     print i, v...0 tic1 tac2 toe

如果要同时循环两个或多个序列，可以用zip()函数。

>>> questions = ['name', 'quest', 'favorite color']>>> answers = ['lancelot', 'the holy grail', 'blue']>>> for q, a in zip(questions, answers):...     print 'What is your {0}?  It is {1}.'.format(q, a)...What is your name?  It is lancelot.What is your quest?  It is the holy grail.What is your favorite color?  It is blue.

如果要倒序循环一个序列，用reversed()函数。

>>> for i in reversed(xrange(1,10,2)):...     print i...97531

在字典中循环的时候，关键字和值可以同时检索，用iteritems()函数。

>>> knights = {'gallahad': 'the pure', 'robin': 'the brave'}>>> for k, v in knights.iteritems():...     print k, v...gallahad the purerobin the brave