你應該使用Python3里的這些新特性
- 2020 年 1 月 2 日
- 筆記
概述
由於Python2的官方維護期即將結束,越來越多的Python項目從Python2切換到了Python3。可是,在實際的工作中,我發現好多人都是在用Python2的思維去寫Python3的程式碼,Python3給我們提供了很多新的、很方便的特性,可以幫助我們快速的編寫程式碼。
f-strings (3.6+)
在Python裡面,我們經常使用format函數來格式化字元串,例如:
user = "Jane Doe" action = "buy" log_message = 'User {} has logged in and did an action {}.'.format( user, action ) print(log_message) 輸出:User Jane Doe has logged in and did an action buy.
Python3裡面提供了一個更加靈活方便的方法來格式化字元串,叫做f-strings。上面的程式碼可以這樣實現:
user = "Jane Doe" action = "buy" log_message = f'User {user} has logged in and did an action {action}.' print(log_message) 輸出: User Jane Doe has logged in and did an action buy.
Pathlib (3.4+)
f-strings這個功能太方便了,但是對於文件路勁這樣的字元串,Python還提供了更加方便的處理方法。Pathlib是Python3提供的一個處理文件路勁的庫。例如:
from pathlib import Path root = Path('post_sub_folder') print(root) 輸出結果: post_sub_folder path = root / 'happy_user' # 輸出絕對路勁 print(path.resolve()) 輸出結果:/root/post_sub_folder/happy_user
Type hinting (3.5+)
靜態與動態類型是軟體工程中的一個熱門話題,每個人都有不同的看法,Python作為一個動態類型語言,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類讓你很容就能實現一個枚舉類型:
from enum import Enum, auto class Monster(Enum): ZOMBIE = auto() WARRIOR = auto() BEAR = auto() print(Monster.ZOMBIE) 輸出: Monster.ZOMBIE
Python3的Enum還支援比較和迭代。
for monster in Monster: print(monster) 輸出: Monster.ZOMBIE Monster.WARRIOR Monster.BEAR
Built-in LRU cache (3.2+)
快取是現在的軟體領域經常使用的技術,Python3提供了一個lru_cache裝飾器,來讓你更好的使用快取。下面有個實例:
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
現在我們可以使用lru_cache來優化我們上面的程式碼,降低程式碼執行時間。
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+)
廢話不多說,直接上程式碼,文檔在這
head, *body, tail = range(5) print(head, body, tail) 輸出: 0 [1, 2, 3] 4 py, filename, *cmds = "python3.7 script.py -n 5 -l 15".split() print(py) print(filename) print(cmds) 輸出:python3.7 script.py ['-n', '5', '-l', '15'] first, _, third, *_ = range(10) print(first, third) 輸出: 0 2
Data classes (3.7+)
Python3提供data class裝飾器來讓我們更好的處理數據對象,而不用去實現 init__() 和 __repr() 方法。假設如下的程式碼:
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實現上面功能的程式碼,這麼寫:
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+)
通常情況下,Python通過把程式碼打成包(在目錄中加入__init__.py實現)來複用,官方給的示例如下:
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,如上的目錄結構,每個目錄都必須有__init__.py文件,一遍其他模組調用目錄下的python程式碼,在Python3里,通過 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
結語
這篇文章只列出了一下部分Python3的新功能,我希望這篇文章向您展示了部分您以前不知道的Python 3新功能,並且希望能幫助您編寫更清晰,更直觀的程式碼。