Python typing —— 类型提示（type hint）

• https://www.rddoc.com/doc/Python/3.6.0/zh/library/typing/

1. 基础类型

• 指定参数类型和返回值类型：

  def greeting(name: str) -> str:
  	return 'hello ' + name
  

• 序列

  def scale(scalar: float, vector: list) -> list:
      return [scalar * num for num in vector]
  >> scale(3, [1, 2, 3])
  [3, 6, 9]
  

  但 list 本身是一个容器，对其内的元素是没有类型限制的，如果我们想指定元素类型为 float 的 list；

2. List、Tuple 与 Dict

• 元素类型为 float 的 list；

  from typing import List, Tuple, Dict
  
  def scale(scalar: float, vector: List[float]) -> List[float]:
      return [scalar * num for num in vector]
  

• 使用别名以简化复杂函数签名：

  from typing import Dict, Tuple, List
  
  ConnectionOptions = Dict[str, str]
  	# str 类型的 key，str 类型的 value
  Address = Tuple[str, int]
  	# 二元 tuple
  Server = Tuple[Address, ConnectionOptions]
  
  def broadcast_message(message: str, servers: List[Server]) -> None:
      ...
  
  # The static type checker will treat the previous type signature as
  # being exactly equivalent to this one.
  def broadcast_message(
          message: str,
          servers: List[Tuple[Tuple[str, int], Dict[str, str]]]) -> None:
      ...