首页手记你应该使用Python3里的这些新特性

你应该使用Python3里的这些新特性

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Python

本文翻译自：http://datawhatnow.com/things-you-are-probably-not-using-in-python-3-but-should/
原文作者：Vinko Kodžoman

概述

由于Python2的官方维护期即将结束，越来越多的Python项目从Python2切换到了Python3。可是，在实际的工作中，我发现好多人都是在用Python2的思维去写Python3的代码，Python3给我们提供了很多新的、很方便的特性，可以帮助我们快速的编写代码。

f-strings (3.6+)

在Python里面，我们经常使用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，叫做f-strings。上面的代码可以这样实现:


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，但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，每个人都有不同的看法，Python作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+)

缓存是现在的软件领域经常使用的技术，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

现在我们可以使用lru_cache来优化我们上面的代码，降低代码执行时间。


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+)

废话不多说，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装饰器来让我们更好的处理数据对象，而不用去实现 init() 和 repr() 方法。假设如下的代码:


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+)

通常情况下，Python通过把代码打成包（在目录中加入__init__.py实现）来复用，官方给的示例如下:


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，每个目录都必须有__init__.py文件，一遍其他模块调用目录下的python代码，在Python3里，通过 Implicit Namespace Packages可是不使用_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