5.6. 循环技巧
最后更新于：2022-04-01 00:48:00
在字典中循环时，关键字和对应的值可以使用 iteritems() 方法同时解读出来:
~~~
>>> knights = {'gallahad': 'the pure', 'robin': 'the brave'}
>>> for k, v in knights.items():
... print(k, v)
...
gallahad the pure
robin the brave
~~~
在序列中循环时，索引位置和对应值可以使用 enumerate() 函数同时得到:
~~~
>>> for i, v in enumerate(['tic', 'tac', 'toe']):
... print(i, v)
...
0 tic
1 tac
2 toe
~~~
同时循环两个或更多的序列，可以使用 zip() 整体打包:
~~~
>>> 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.
~~~
需要逆向循环序列的话，先正向定位序列，然后调用 reversed() 函数:
~~~
>>> for i in reversed(range(1, 10, 2)):
... print(i)
...
9
7
5
3
1
~~~
要按排序后的顺序循环序列的话，使用 sorted() 函数，它不改动原序列，而是生成一个新的已排序的序列:
~~~
>>> basket = ['apple', 'orange', 'apple', 'pear', 'orange', 'banana']
>>> for f in sorted(set(basket)):
... print(f)
...
apple
banana
orange
pear
~~~