python中很酷的技能(上)

参考：https://www.quora.com/Python-programming-language-1/What-are-some-cool-Python-tricks

1.几个简单的

产生一个数组 

[10 * x for x in a]

 产生一个迭代（a generatorexpression）

(10 * x for x in a)

 dict和set

>>> {x: 10 * x for x in range(5)}
{0: 0, 1: 10, 2: 20, 3: 30, 4: 40}
>>> {10 * x for x in range(5)}
set([0, 40, 10, 20, 30])

2.最快的速度将本地文件共享到网上

python -m SimpleHTTPServer

3.文件中最长的一行

max(open('test.txt'), key=len) 

4.无穷大和无穷小

float('Inf')
float('-Inf')

 5.比大小

3 > x == 1
-> False

 6.循环中找index

mylist = [4,2,42]
for i, value in enumerate(mylist):
    print i, ': ', value
-> 0: 4
-> 1: 2
-> 2: 42

7.'*'的用途

def foo(a, b, c):
    print a, b, c

mydict = {'a':1, 'b':2, 'c':3}
mylist = [10, 20, 30]

foo(*mydict)
-> a, b, c
foo(**mydict)
-> 1, 2, 3
foo(*mylist)
-> 10 20 30

a,*b ="python
-> a='p' b=('y','t','h','o','n')

 8.简单枚举

class PlayerRanking:
  Bolt, Green, Johnson, Mom = range(4)

PlayerRanking.Mom
-> 4

 9.交换两个数值

b, a = a, b

10.翻转数组和字符串

"Hello world"[::-1]
[1,2,3][::-1]
[1,2,3].reverse()

11.自动关闭文件流

with open("my_file.txt") as f:
   print(f.readlines())

 在这两句代码执行后，文件被自动关闭。