python3新特性

介绍

之前断断续续的看过一点python3新特性，今天在这里给大家总结一下。

环境

Python 3.7.3
Mac 10.15.1

实操

1. 格式化字符串f-string

In [1]: a = "my is str"
In [2]: f"{a}"
Out[2]: 'my is str'

In [4]: b = {"user": "qingge"}
In [6]: f"{b['user']}"
Out[6]: 'qingge'

2. 类型提示Type hinting

In [7]: def ret_str(a:str) -> bool:
   ...:     return a in "abc"
   ...:

In [8]: ret_str("c")
Out[8]: True

3. 枚举类enum

• 自定义枚举值

In [9]: from enum import Enum, auto

In [16]: class Color(Enum):
    ...:     RED = 1
    ...:     BlUE = 2
    ...:     GREEN = 3

In [17]: list(Color)
Out[17]: [<Color.RED: 1>, <Color.BlUE: 2>, <Color.GREEN: 3>]

• 自增，自定义自增值

In [18]: class AutoName(Enum):
    ...:     def _generate_next_value_(name, start, count, last_values):
    ...:         return name
    ...:

In [19]: class Color(AutoName):
    ...:     RED = auto()
    ...:     BlUE = auto()
    ...:     GREEN = auto()
    ...:

In [20]: list(Color)
Out[20]: [<Color.RED: 'RED'>, <Color.BlUE: 'BlUE'>, <Color.GREEN: 'GREEN'>]

• 访问方式

In [21]: red = Color.RED

In [22]: red
Out[22]: <Color.RED: 'RED'>

In [23]: red = Color.RED.value

In [24]: red
Out[24]: 'RED'

In [26]: for key, value in Color.__members__.items():
    ...:     print(f"key:value => {key}:{value}")
    ...:
key:value => RED:Color.RED
key:value => BlUE:Color.BlUE
key:value => GREEN:Color.GREEN

4. itertools模块

• count

In [40]: from itertools import count

In [41]: for i in count(1):
    ...:     if i > 10:
    ...:         break
    ...:     else:
    ...:         print(i)
    ...:
1
2
3
4
5
6
7
8
9
10

• cycle

In [45]: from itertools import cycle
In [45]: for i in cycle('A'):
    ...:     print(i)
A
A
A
A
A
A
...

更多的函数，大家可以自己尝试
repeat
chain()     p, q, ...           p0, p1, ... plast, q0, q1, ...              chain('ABC', 'DEF') --> A B C D E F

compress()  data, selectors     (d[0] if s[0]), (d[1] if s[1]), ...     

compress('ABCDEF', [1,0,1,0,1,1]) --> A C E F

dropwhile() pred, seq           seq[n], seq[n+1], starting when pred fails  

dropwhile(lambda x: x<5, [1,4,6,4,1]) --> 6 4 1

groupby()   iterable[, keyfunc] sub-iterators grouped by value of keyfunc(v)

ifilter()   pred, seq           elements of seq where pred(elem) is True    

ifilter(lambda x: x%2, range(10)) --> 1 3 5 7 9

ifilterfalse()  pred, seq       elements of seq where pred(elem) is False   

ifilterfalse(lambda x: x%2, range(10)) --> 0 2 4 6 8

islice()    seq, [start,] stop [, step] elements from seq[start:stop:step]  

islice('ABCDEFG', 2, None) --> C D E F G

imap()      func, p, q, ...     func(p0, q0), func(p1, q1), ...             imap(pow, (2,3,10), (5,2,3)) --> 32 9 1000

starmap()   func, seq           func(*seq[0]), func(*seq[1]), ...           starmap(pow, [(2,5), (3,2), (10,3)]) --> 32 9 1000

tee()       it, n               it1, it2 , ... itn splits one iterator into n

takewhile() pred, seq           seq[0], seq[1], until pred fails            

takewhile(lambda x: x<5, [1,4,6,4,1]) --> 1 4

izip()      p, q, ...           (p[0], q[0]), (p[1], q[1]), ...             izip('ABCD', 'xy') --> Ax By

izip_longest()  p, q, ...       (p[0], q[0]), (p[1], q[1]), ...             izip_longest('ABCD', 'xy', fillvalue='-') --> Ax By C- D-

5. LRU缓存，memoization技术

In [46]: from functools import lru_cache
In [46]: from functools import lru_cache

In [47]: @lru_cache(maxsize=512)
    ...: def fib_memoization(number:int) -> int:
    ...:     if number ==0 : return 0
    ...:     if number ==1 : return 1
    ...:     return fib_memoization(number - 1)

In [49]: import time

In [50]: start = time.time()

In [51]: fib_memoization(40)
Out[51]: 1

In [52]: print(f'Duration:{time.time() - start}s')
Duration:13.406868934631348s

6. 分解迭代扩展包

In [53]: a, *b, c = range(5)

In [54]: print(a, b, c)
0 [1, 2, 3] 4

7. dataclass

Data class装饰器，用来减少对样板代码的使用，该装饰器会自动生成init()和repr()方法。

class Armor:
    def __init__(self, armor:float, description:str, level:int = 1):
        self.armor = armor
        self.level = level
        self.description = description
    
    def power(self) -> float:
        return self.armor * self.level

armor = Armor(5.2, "common armor.", 2)
armor.power() #10.4


###使用Data Class实现相同的Armor类
from dataclasses import dataclass
@dataclass
class Armor:
    armor : float
    description : str
    level : int = 1

    def power(self) -> float:
        return self.armor *self.level

armor = Armor(5.2, "common armor.", 2)
armor.power()

8. bisect模块保持列表排序：

这是一个免费的二分查找实现和快速插入有序序列的工具。也就是说，你可以使用：

import bisect
bisect.insort(list, element)

9. typing

类型检查，防止运行时出现参数和返回值类型不符合。
作为开发文档附加说明，方便使用者调用时传入和返回参数类型。
该模块加入后并不会影响程序的运行，不会报正式的错误，只有提醒。
**注意：typing模块只有在python3.5以上的版本中才可以使用,pycharm目前支持typing检查OK **

• int,long,float: 整型,长整形,浮点型;
• bool,str: 布尔型，字符串类型；
• List, Tuple, Dict, Set:列表，元组，字典, 集合;
• Iterable,Iterator:可迭代类型，迭代器类型；
• Generator：生成器类型；

In [63]: from typing import List, Tuple, Dict

In [64]: def add(a:int, string:str, f:float, b:bool) -> Tuple[List, Tuple, Dict, bool]:
    ...:     list1 = list(range(a))
    ...:     tup = (string, string, string)
    ...:     d = {"a":f}
    ...:     bl = b
    ...:     return list1, tup, d, bl
    ...:
    ...:
    ...:

In [65]: add(5,"hhhh", 2.3, False)
Out[65]: ([0, 1, 2, 3, 4], ('hhhh', 'hhhh', 'hhhh'), {'a': 2.3}, False)

10. 路径管理库 Pathlib

In [68]: from pathlib import Path

In [69]: root = Path('test_path')

In [70]: root
Out[70]: PosixPath('test_path')

In [71]: path = root / 'test_path'

In [72]: path.resolve()
Out[72]: PosixPath('/Users/caiqing/Desktop/test_path/test_path')