[python]Looping Techniques / 循环的技巧

https://docs.python.org/zh-cn/3/tutorial/datastructures.html#tut-loopidioms

 

当在字典中循环时，用 items() 方法可将关键字和对应的值同时取出

>>>

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

当在序列中循环时，用 enumerate() 函数可以将索引位置和其对应的值同时取出

>>>

>>> for i, v in enumerate(['tic', 'tac', 'toe']): ... print(i, v) ... 0 tic 1 tac 2 toe 

当同时在两个或更多序列中循环时，可以用 zip() 函数将其内元素一一匹配。

>>>

>>> 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. 

当逆向循环一个序列时，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 

如果要按某个指定顺序循环一个序列，可以用 sorted() 函数，它可以在不改动原序列的基础上返回一个新的排好序的序列

>>>

>>> basket = ['apple', 'orange', 'apple', 'pear', 'orange', 'banana'] >>> for f in sorted(set(basket)): ... print(f) ... apple banana orange pear 

有时可能会想在循环时修改列表内容，一般来说改为创建一个新列表是比较简单且安全的

>>>

>>> import math
>>> raw_data = [56.2, float('NaN'), 51.7, 55.3, 52.5, float('NaN'), 47.8] >>> filtered_data = [] >>> for value in raw_data: ... if not math.isnan(value): ... filtered_data.append(value) ... >>> filtered_data [56.2, 51.7, 55.3, 52.5, 47.8]

转载于:https://www.cnblogs.com/alfredsun/p/10978725.html