迭代函数：zip、enumerate，list解析

#encoding:utf-8
"""
并行迭代：
    zip
    enumerate
        获取元素及下标
    list解析
    iter
"""

#zip
# 两个长度相同的列表，求对应元素的和

# 原始做法：
# 当两个元素长度不一致时，这个程序就会出问题,zip可以避免这个问题
def zip_test():
    a,b = [1,2,3,4,5],[9,8,7,6,5]
    c= []
    # for i in range(len(a)):
    #     c.append(a[i] + b[i])
    # return c

    # 改进
    length = len(a) if len(a)<len(b) else len(b)
    for i in range(length):
        c.append(a[i] + b[i])
    return c

#zip实现
def zip_test2():
    a,b = [1,2,3,4,5],[9,8,7,6,5]
    c = []
    lst = zip(a,b)
    print lst
    for x,y in lst:
        c.append(x+y)
    return c

# zip优化
def zip_test3():
    a,b = [1,2,3,4,5],[9,8,7,6,5]
    return [x+y for x,y in zip(a,b)]

#list长度不一，zip获取
def zip_test4():
    a= [1,2,3]
    b=[11,12,13,14,15]
    return zip(a,b)    # 结果：[(1, 11), (2, 12), (3, 13)]

# 字典执行zip，key视序列，将序列对应的元素一次组成元组，做一个list的元素
def zip_test5():
    s = {'name':'bob'}
    t = {'language':'python'}
    return zip(s,t)    #结果：[('name', 'language')]

# 颠倒字典的key value的例子
# 方法1:for循环
def zip_test6():
    myinfor = {"name":"bob","site":"www.google.com","language":"python"}
    new_infor = {}
    for k,v in myinfor.items():
        new_infor[v] = k
    return new_infor

# 方法2：zip
def zip_test7():
    myinfor = {"name":"bob","site":"www.google.com","language":"python"}
    return dict(zip(myinfor.values(),myinfor.keys()))

# zip的参数 *iterables
def zip_test8():
    list1 = [2,4,6,8]
    list2 = [11,13,15,17]
    result = zip(list1,list2)
    print result    #[(2, 11), (4, 13), (6, 15), (8, 17)]
    return zip(*result)    #[(2, 4, 6, 8), (11, 13, 15, 17)]

# enumerate
def enumerate_test():
    week = ['monday','sunday','friday']
    for i in range(len(week)):
        print week[i] + " is " +str(i)

# enumerate的方式实现
def enumerate_test2():
    week = ['monday','sunday','friday']
    for i ,m in enumerate(week):
        print week[i] + " is " +str(i)

if __name__ =="__main__":
    print "-------zip-------"
    print zip_test()
    print zip_test2()
    print zip_test3()
    print zip_test4()
    print zip_test5()
    print zip_test6()
    print zip_test7()
    print zip_test8()
    print "------enumerate----"
    enumerate_test()
    enumerate_test2()

结果：

-------zip-------
[, , , , ]
[(, ), (, ), (, ), (, ), (, )]
[, , , , ]
[, , , , ]
[(, ), (, ), (, )]
[('name', 'language')]
{'python': 'language', 'bob': 'name', 'www.google.com': 'site'}
{'python': 'language', 'bob': 'name', 'www.google.com': 'site'}
[(, ), (, ), (, ), (, )]
[(, , , ), (, , , )]
------enumerate----
monday is
sunday is
friday is
monday is
sunday is
friday is