你应该使用Python3里的这些新特性

概述

因为Python2的官方维护期即将结束，愈来愈多的Python项目从Python2切换到了Python3。但是，在实际的工做中，我发现好多人都是在用Python2的思惟去写Python3的代码，Python3给咱们提供了不少新的、很方便的特性，能够帮助咱们快速的编写代码。

f-strings (3.6+)

在Python里面，咱们常常使用format函数来格式化字符串，例如：

user = "Jane Doe"
action = "buy"

log_message = 'User {} has logged in and did an action {}.'.format(
  user,
  action
)

print(log_message)
输出：User Jane Doe has logged in and did an action buy.

Python3里面提供了一个更加灵活方便的方法来格式化字符串，叫作f-strings。上面的代码能够这样实现:

user = "Jane Doe"
action = "buy"

log_message = f'User {user} has logged in and did an action {action}.'
print(log_message)
输出: User Jane Doe has logged in and did an action buy.

Pathlib (3.4+)

f-strings这个功能太方便了，可是对于文件路劲这样的字符串，Python还提供了更加方便的处理方法。Pathlib是Python3提供的一个处理文件路劲的库。例如：

from pathlib import Path

root = Path('post_sub_folder')
print(root)
输出结果: post_sub_folder

path = root / 'happy_user'

# 输出绝对路劲
print(path.resolve())
输出结果：/root/post_sub_folder/happy_user

Type hinting (3.5+)

静态与动态类型是软件工程中的一个热门话题，每一个人都有不一样的见解，Python做为一个动态类型语言，在Python3中也提供了Type hinting功能，例如:

def sentence_has_animal(sentence: str) -> bool:
  return "animal" in sentence

sentence_has_animal("Donald had a farm without animals")
# True

Enumerations (3.4+)

Python3提供的Enum类让你很容就能实现一个枚举类型：

from enum import Enum, auto

class Monster(Enum):
    ZOMBIE = auto()
    WARRIOR = auto()
    BEAR = auto()
    
print(Monster.ZOMBIE)
输出: Monster.ZOMBIE

Python3的Enum还支持比较和迭代。

for monster in Monster:
    print(monster)

输出: Monster.ZOMBIE
     Monster.WARRIOR
     Monster.BEAR

Built-in LRU cache (3.2+)

缓存是如今的软件领域常常使用的技术，Python3提供了一个lru_cache装饰器，来让你更好的使用缓存。下面有个实例：

import time

def fib(number: int) -> int:
    if number == 0: return 0
    if number == 1: return 1
    
    return fib(number-1) + fib(number-2)

start = time.time()
fib(40)
print(f'Duration: {time.time() - start}s')
# Duration: 30.684099674224854s

如今咱们可使用lru_cache来优化咱们上面的代码，下降代码执行时间。

from functools import lru_cache

@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) + fib_memoization(number-2)

start = time.time()
fib_memoization(40)
print(f'Duration: {time.time() - start}s')
# Duration: 6.866455078125e-05s

Extended iterable unpacking (3.0+)

废话很少说，直接上代码，文档在这

head, *body, tail = range(5)
print(head, body, tail)
输出： 0 [1, 2, 3] 4

py, filename, *cmds = "python3.7 script.py -n 5 -l 15".split()
print(py)
print(filename)
print(cmds)
输出：python3.7
     script.py
     ['-n', '5', '-l', '15']

first, _, third, *_ = range(10)
print(first, third)
输出： 0 2

Data classes (3.7+)

Python3提供data class装饰器来让咱们更好的处理数据对象，而不用去实现 init__() 和 __repr() 方法。假设以下的代码:

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

print(armor)
# <__main__.Armor object at 0x7fc4800e2cf8>

使用data class实现上面功能的代码，这么写:

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()
# 10.4

print(armor)
# Armor(armor=5.2, description='Common armor.', level=2)

Implicit namespace packages (3.3+)

一般状况下，Python经过把代码打成包（在目录中加入__init__.py实现）来复用，官方给的示例以下:

sound/                          Top-level package
      __init__.py               Initialize the sound package
      formats/                  Subpackage for file format conversions
              __init__.py
              wavread.py
              wavwrite.py
              aiffread.py
              aiffwrite.py
              auread.py
              auwrite.py
              ...
      effects/                  Subpackage for sound effects
              __init__.py
              echo.py
              surround.py
              reverse.py
              ...
      filters/                  Subpackage for filters
              __init__.py
              equalizer.py
              vocoder.py
              karaoke.py

在Python2里，如上的目录结构，每一个目录都必须有__init__.py文件，一遍其余模块调用目录下的python代码，在Python3里，经过 Implicit Namespace Packages但是不使用__init__.py文件

sound/                          Top-level package
      __init__.py               Initialize the sound package
      formats/                  Subpackage for file format conversions
              wavread.py
              wavwrite.py
              aiffread.py
              aiffwrite.py
              auread.py
              auwrite.py
              ...
      effects/                  Subpackage for sound effects
              echo.py
              surround.py
              reverse.py
              ...
      filters/                  Subpackage for filters
              equalizer.py
              vocoder.py
              karaoke.py

结语

这篇文章只列出了一下部分Python3的新功能，我但愿这篇文章向您展现了部分您之前不知道的Python 3新功能，而且但愿能帮助您编写更清晰，更直观的代码。