Python系列教程(十一):遍历

遍历

通过for ... in ...:或者while的语法结构，将字符串、列表、元组、字典等数据结构中的元素循环输出，这种方式就是遍历。

注意python语法的缩进

1.1 字符串遍历

示例1:

a_str = "hello"
for char in a_str:
    print(char)

结果:

h
e
l
l
o

示例2:

a_str = "hello"

length = len(a_str )

i = 0

while i<length:
    print(a_str [i])
    i+=1

结果:

xiaoWang
xiaoZhang
xiaoHua

1.2 列表遍历

示例1:

namesList = ['xiaoWang','xiaoZhang','xiaoHua']
for name in namesList:
    print(name)

结果:

xiaoWang
xiaoZhang
xiaoHua

示例2:

namesList = ['xiaoWang','xiaoZhang','xiaoHua']

length = len(namesList)

i = 0

while i<length:
    print(namesList[i])
    i+=1

结果:

xiaoWang
xiaoZhang
xiaoHua

1.3 元组遍历

示例1:

a_turple = ['xiaoWang','xiaoZhang','xiaoHua']
for name in a_turple :
    print(name)

结果:

xiaoWang
xiaoZhang
xiaoHua

示例2:

a_turple = ['xiaoWang','xiaoZhang','xiaoHua']

length = len(a_turple )

i = 0

while i<length:
    print(a_turple[i])
    i+=1

结果:

h
e
l
l
o

1.4 字典遍历

<1> 遍历字典的key（键）

dict = {'name':'wang','sex':'m','age':20}
for key in dict.keys():
	print(key)

结果：

age
name
sex

<2> 遍历字典的value（值）

dict = {'name':'wang','sex':'m','age':20}
for value in dict.values():
	print(value)

结果：

20
wang
m

<3> 遍历字典的项（元素）

dict = {'name':'wang','sex':'m','age':20}
for item in dict.items():
	print(item) 

结果：

('age', 20)
('name', 'wang')
('sex', 'm')

<4> 遍历字典的key-value（键值对）

dict = {'name':'wang','sex':'m','age':20}
for key, value in dict.items():
	print(key,value)

结果：

sex m
name wang
age 20

1.5 集合遍历

示例1:

set= set(['a', 'b', 'c', 'd'])
for s in set:
    print (s)

结果:

c
d
a
b

示例2:

a_set = (['a', 'b', 'c', 'd'])

length = len(a_set)

i = 0

while i<length:
    print(a_set[i])
    i+=1

结果:

a
b
c
d