高级特性

标签：python

1.切片

L = [‘Michael‘,‘Sarah‘,‘Tracy‘,‘Bob‘,‘Jack‘]

L[0:3] #从0开始索引，直到3，但不包括3，也就是0,1,2

[‘Michael‘, ‘Sarah‘, ‘Tracy‘]

L[:3] #如果索引从0开始，可以忽略

[‘Michael‘, ‘Sarah‘, ‘Tracy‘]

L[-1] #取倒数第一个元素

[‘Jack‘]

L = range(100)

L

[0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99]

L[:10] #取前10个数

[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]

L[-10:] #取后10个数

[90, 91, 92, 93, 94, 95, 96, 97, 98, 99]

L[10:20] #取10-20

[10, 11, 12, 13, 14, 15, 16, 17, 18, 19]

L[:10:2] #前10个数，每2个取一个

[0, 2, 4, 6, 8]

L[::5] #所有数里面，每5个取一个

[0, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95]

2.迭代

字典迭代

d = {‘a‘:1,‘b‘:2,‘c‘:3}

d

{‘a‘: 1, ‘c‘: 3, ‘b‘: 2}

for key in d:

    print key

a

c

b

for key in d:

    print key,d[key] 

a 1

c 3

b 2

for value in d.itervalues(): #迭代values

    print value

1

3

2

for k,v in d.iteritems(): #迭代k和v

    print k,v

a 1

c 3

b 2

3.列表生成式

range(1,11)

[1, 2, 3, 4, 5, 6, 7, 8, 9, 10]

L = []

for x in range(1,11):

    L.append(x*x) 

L

[1, 4, 9, 16, 25, 36, 49, 64, 81, 100]

L = [x*x for x in range(1,11)]

[1, 4, 9, 16, 25, 36, 49, 64, 81, 100]

d = {‘x‘:‘A‘,‘y‘:‘B‘,‘z‘:‘C‘}

l = [k + ‘=‘ + v for k,v in d.iteritems()]

4.生成器

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

L

[0, 1, 4, 9, 16, 25, 36, 49, 64, 81]

g = (x * x for x in range(10))

g

<generator object <genexpr> at 0x104feab40>

g.next() #取值

g = (x*x for x in range(10))

for n in g: #可以迭代，这种是最有效的方式

    print n

本文出自 “八英里” 博客，请务必保留此出处http://5921271.blog.51cto.com/5911271/1795925

高级特性

标签：python

原文地址：http://5921271.blog.51cto.com/5911271/1795925