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你应该使用Python3里的这些新特性

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:

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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:

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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:

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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:

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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:

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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。

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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:

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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。

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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

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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:

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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:

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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:

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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

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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,我希望这篇文章向您展示了部分您以前不知道的Python 3新功能,并且希望能帮助您编写更清晰,更直观的代码。