学习python(四)

学习http://www.cnblogs.com/vamei/archive/2012/07/09/2582435.html

1. 利用range(), 得到下标

S = 'abcdefghijk'
for i in range(0,len(S),2):
    print S[i]

2. 利用 enumerate() , 同时得到 下标和元素

S = 'abcdefghijk'
for (index,char) in enumerate(S):
    print index
    print char

3. 利用 zip() , 实现 并行循环

ta = [1,2,3]
tb = [9,8,7]

# cluster
zipped = zip(ta,tb)
print(zipped)

# decompose
na, nb = zip(*zipped)
print(na, nb)

4.生成器

def gen():
    a = 100
    yield a
    a = a*8
    yield a
    yield 1000

for i in gen():
    print i

yield

def gen():
    for i in range(4):
        yield i

==

G = (x for x in range(4))

L = []
for x in range(10):
    L.append(x**2)
==

L = [x**2 for x in range(10)]

xl = [1,3,5]
yl = [9,12,13]
L  = [ x**2 for (x,y) in zip(xl,yl) if y > 10] [9,25]