交换变量

x = 6 y = 5 x, y = y, x print x

5 print y 6

if 语句在行内

print “Hello” if True else “World”

Hello

连接
下面的最后一种方式在绑定两个不同类型的对象时显得很酷。

nfc = [“Packers”, “49ers”] afc = [“Ravens”, “Patriots”] print nfc + afc

[‘Packers’, ‘49ers’, ‘Ravens’, ‘Patriots’]

print str(1) + “ world”

1 world

print 1 + “ world”

1 world

print 1, “world”

1 world print nfc, 1 [‘Packers’, ‘49ers’] 1

计算技巧

向下取整

print 5.0//2

2

2的5次方

print 2**5

32

注意浮点数的除法

print .3/.1

2.9999999999999996 print .3//.1 2.0

数值比较

x = 2 if 3 > x > 1: print x

2 if 1 < x > 0: print x 2

两个列表同时迭代

nfc = [“Packers”, “49ers”] afc = [“Ravens”, “Patriots”] for teama, teamb in zip(nfc, afc): print teama + “ vs. “ + teamb

Packers vs. Ravens 49ers vs. Patriots

带索引的列表迭代

teams = [“Packers”, “49ers”, “Ravens”, “Patriots”] for index, team in enumerate(teams): print index, team

0 Packers 1 49ers 2 Ravens 3 Patriots

列表推导
已知一个列表，刷选出偶数列表方法：

numbers = [1,2,3,4,5,6] even = [] for number in numbers: if number%2 == 0: even.append(number)

用下面的代替

numbers = [1,2,3,4,5,6] even = [number for number in numbers if number%2 == 0]

字典推导

teams = [“Packers”, “49ers”, “Ravens”, “Patriots”] print {key: value for value, key in enumerate(teams)}

{‘49ers’: 1, ‘Ravens’: 2, ‘Patriots’: 3, ‘Packers’: 0}

初始化列表的值

items = [0]*3 print items

[0,0,0]

将列表转换成字符串

teams = [“Packers”, “49ers”, “Ravens”, “Patriots”] print “, “.join(teams)

‘Packers, 49ers, Ravens, Patriots’

从字典中获取元素
不要用下列的方式

data = {‘user’: 1, ‘name’: ‘Max’, ‘three’: 4} try: is_admin = data[‘admin’] except KeyError: is_admin = False

替换为

data = {‘user’: 1, ‘name’: ‘Max’, ‘three’: 4} is_admin = data.get(‘admin’, False)

获取子列表

x = [1,2,3,4,5,6]

前3个

print x[:3]

[1,2,3]

中间4个

print x[1:5] [2,3,4,5]

最后3个

print x[-3:] [4,5,6]

奇数项

print x[::2] [1,3,5]

偶数项

print x[1::2] [2,4,6]

60个字符解决FizzBuzz
前段时间Jeff Atwood 推广了一个简单的编程练习叫FizzBuzz，问题引用如下：

写一个程序，打印数字1到100，3的倍数打印“Fizz”来替换这个数，5的倍数打印“Buzz”，对于既是3的倍数又是5的倍数的数字打印“FizzBuzz”。

这里有一个简短的方法解决这个问题：

for x in range(101):print”fizz”[x%34::]+”buzz”[x%54::]or x

集合
用到Counter库

from collections import Counter print Counter(“hello”)

Counter({‘l’: 2, ‘h’: 1, ‘e’: 1, ‘o’: 1})

迭代工具
和collections库一样，还有一个库叫itertools

from itertools import combinations teams = [“Packers”, “49ers”, “Ravens”, “Patriots”] for game in combinations(teams, 2): print game

(‘Packers’, ‘49ers’) (‘Packers’, ‘Ravens’) (‘Packers’, ‘Patriots’) (‘49ers’, ‘Ravens’) (‘49ers’, ‘Patriots’) (‘Ravens’, ‘Patriots’) False == True

在python中，True和False是全局变量，因此：

False = True if False: print “Hello” else: print “World”

Hello