python遍历

#coding=utf-8
#!/usr/bin/python3

vec = [2,4,6]

x = [3 * x for x in vec]

print x

x = [[x,x ** 2] for x in vec]

print x

1.对序列里每一个元素逐一调用某方法

freshfruit = ['  banana', '  loganberry ', 'passion fruit  ']

x = [x.strip() for x in freshfruit] #将元素的每个元素去除空格
print x 

2.还可以用if 语句作为过滤器

x = [3 * x for x in vec if x > 3] # 这句话的含义是 如果x > 3  将x * 3 生成新数组

print x # [12,18]

vec1 = [2,4,6]
vec2 = [1,3,5]

x = [ x * y for x in vec1 for y in vec2 if y > x] # 此时只有 3对符合要求  x= 2 y = 3, x= 2 y = 5, x = 4 y= 10

print x # [6,10,20]

3.del关键字的使用

a = [-1, 1, 66.25, 333, 333, 1234.5]

del a[2:4]

print a 

a = [-1, 1, 66.25, 333, 333, 1234.5] ## 从第2个元素开始到第4个元素截止 不包含第四个元素
del a[1:3]

print a

4.如果创建空集合必须用set()

x = set()

5.字典的遍历

dic1 = {"url":"www.baidu.com","address":"nanping"}

for k,v in dic1.items():
    print (k,v)

6.数组的遍历

list1 = ["ac","bc","cc","dc","ec"]

for index,item in enumerate(list1):
    print (index,item) # 打印出索引和元素

7.同时遍历两个或更多的序列，可以使用 zip() 组合

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))
    # print('what is your %s? it is %s' %(q,a)) 也可以用这种方式

    s = 'what is your %s? it is %s' %(q,a) #

    print type(s) # str

8.反向遍历 如果数据是根据时间存储的。我们取出的时候 最后存的放在最下面了。这时候反向遍历就很有用

for i in reversed(range(10)): # 反向遍历
    print i