在字典中循环时,关键字和对应的值可以使用 >>> 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
若要在循环内部修改正在遍历的序列(例如复制某些元素),建议您首先制作副本。在序列上循环不会隐式地创建副本。切片表示法使这尤其方便: >>> words = ['cat', 'window', 'defenestrate']
>>> for w in words[:]: # Loop over a slice copy of the entire list.
... if len(w) > 6:
... words.insert(0, w)
...
>>> words
['defenestrate', 'cat', 'window', 'defenestrate']
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