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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