python学习第24课-列表迭代和字典迭代

在python程序开发中，对列表和字典迭代是非常常见的事情。

我们已经知道，python中for循环的基本格式：

for in :

else:

代表变量，代表序列，字符串、列表、字典都是序列。

●列表迭代

for x in []:

执行语句

之前我们学习for循环和range()函数时，实例中的序列使用过列表，也就是说我们已经学习、并且使用过列表迭代，在此不再赘述。

我们之前都是引用一个变量，但是在python的for循环里，同时引用两个变量，是非常常见的。

如果我们要得到列表中元素的值，又要得到该元素对应的index，可以这么做：

for i,value in enumerate(["a","b","c"]):

print(i,value)

#运行结果

0 a

1 b

2 c

●字典迭代

字典一般可以选择对key迭代、对value迭代和对key/value一起迭代。

现在假设有一个字典为d={"a":1,"b":2,"c":3}

①对key迭代

d={"a":1,"b":2,"c":3}

for key in d:

执行语句

②对value迭代

d={"a":1,"b":2,"c":3}

for value in d.values()

执行语句

③对key/value一起迭代

d={"a":1,"b":2,"c":3}

for k,v in d.items():

执行语句

说明：上面values()和items()方法是python字典自带的方法，values()返回的是字典中的键值的迭代器，items()返回的是字典的键值对组成的元组的列表。

实例1：

names={"Tom Zhao":"He is very cute.","Jimmy Qian":"He is very rich.","William Sun":"He is a little bit shy.","John Li":"He is very handsome."}

for key in names:

print(key)

#运行结果

Tom Zhao

Jimmy Qian

William Sun

John Li

实例2：

names={"Tom Zhao":"He is very cute.","Jimmy Qian":"He is very rich.","William Sun":"He is a little bit shy.","John Li":"He is very handsome."}

for key,value in names.items():

print("Name:{} Saying:{}".format(key,value))

#运行结果

Name:Tom ZhaoSaying:He is very cute.

Name:Jimmy QianSaying:He is very rich.

Name:William SunSaying:He is a little bit shy.

Name:John LiSaying:He is very handsome.

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