python常用技巧

1，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 ]

2，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 }

3，枚举 - enumerate

之前我们这样操作：

iterable = 'asdfghjk'
i = 0
for item in iterable:
    print(i, " ", item)
    i += 1

现在我们这样操作：

iterable='asdfghjk'
for i, item in enumerate(iterable):
    print(i, " ", item)

enumerate函数还可以接收第二个参数。就像下面这样：

list(enumerate('abc'))
# [(0, 'a'), (1, 'b'), (2, 'c')]

list(enumerate('abc', 1))
# [(1, 'a'), (2, 'b'), (3, 'c')]

4，字典/集合 生成 

my_dict = {i: i * i for i in range(10)}
# {0: 0, 1: 1, 2: 4, 3: 9, 4: 16, 5: 25, 6: 36, 7: 49, 8: 64, 9: 81}
my_set = {i * 15 for i in range(10)}
# {0, 135, 105, 75, 45, 15, 120, 90, 60, 30}

列表解析

5，交换变量

x = 6

y = 5

 

x , y = y , x

 

print x

>>> 5

print y

>>> 6

6，两个列表同时迭代

nfc = ["Packers", "49ers"]

afc = ["Ravens", "Patriots"]

for teama , teamb in zip ( nfc , afc ) :

     print teama + " vs. " + teamb

>>> Packers vs. Ravens

>>> 49ers vs. Patriots

7，将列表转换成字符串

teams = ["Packers", "49ers", "Ravens", "Patriots"]

print ", " . join ( teams )

>>> 'Packers, 49ers, Ravens, Patriots'

8，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)

9，60个字符解决FizzBuzz

#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”。

for x in range(1, 101):print("Fizz"[x%3*4:]+"Buzz"[x%5*4:] or x)

10，集合  用到Counter库

from collections import Counter

print Counter("hello")

>>> Counter({'l': 2, 'h': 1, 'e': 1, 'o': 1})

11，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' )