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.
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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.
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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
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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
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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
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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
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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
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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
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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
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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>
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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)
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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
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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
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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。
[原文链接](http://www.bugcode.cn/2019/05/20/python3_new_func/)