概述

由于Python2的官方維護期即將結(jié)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(fā)現(xiàn)好多人都是在用Python2的思維去寫Python3的代碼，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代碼。

f-strings (3.6+)

在Python里面，我們經(jīng)常使用format函數(shù)來格式化字符串，例如：

          
            user = "Jane Doe"
action = "buy"

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

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

Python3里面提供了一個更加靈活方便的方法來格式化字符串，叫做f-strings。上面的代碼可以這樣實現(xiàn):

          
            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，但是對于文件路勁這樣的字符串，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(jié)果: post_sub_folder

path = root / 'happy_user'

# 輸出絕對路勁
print(path.resolve())
輸出結(jié)果：/root/post_sub_folder/happy_user
          
        

Type hinting (3.5+)

靜態(tài)與動態(tài)類型是軟件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(tài)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(xiàn)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還支持比較和迭代。

          
            for monster in Monster:
    print(monster)

輸出: Monster.ZOMBIE
     Monster.WARRIOR
     Monster.BEAR
          
        

Built-in LRU cache (3.2+)

緩存是現(xiàn)在的軟件領(lǐng)域經(jīng)常使用的技術(shù)，Python3提供了一個lru_cache裝飾器，來讓你更好的使用緩存。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(xiàn)在我們可以使用lru_cache來優(yōu)化我們上面的代碼，降低代碼執(zhí)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，直接上代碼，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(shù)據(jù)對象，而不用去實現(xiàn) init__() 和 __repr() 方法。假設如下的代碼:

          
            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(xiàn)上面功能的代碼，這么寫:

          
            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通過把代碼打成包（在目錄中加入__init__.py實現(xiàn)）來復用，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(jié)構(gòu)，每個目錄都必須有__init__.py文件，一遍其他模塊調(diào)用目錄下的python代碼，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(jié)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，并且希望能幫助您編寫更清晰，更直觀的代碼。