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 = 6y = 5 x, y = y, x print x>>> 5print 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 Counterprint 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 combinationsteams = ["Packers", "49ers", "Ravens", "Patriots"]for game in combinations(teams, 2):    print game>>> ('Packers', '49ers')>>> ('Packers', 'Ravens')>>> ('Packers', 'Patriots')>>> ('49ers', 'Ravens')>>> ('49ers', 'Patriots')>>> ('Ravens', 'Patriots')

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