01.python_class

Python的类 §

格式化输出类内的数据内容 §

• 使用默认的__repr__方法

 def __repr__(self):
    return "Prop 1: " + str(self.prop1)+", Prop 2: "+str(self.prop2)

构建数据类型（使用dataclass） §

使用dataclass创建复合数据类型 §

• 引用dataclasses的dataclass和field
• list、dict等类型需要使用default_factory初始化

  from dataclasses import dataclass, field
   
  @dataclass
  class TestType:
      str_type: str = None
      np_type: np.ndarray = None
      value_type: float = None
      list_type: list = field(default_factory=lambda: [False]*6)

数据类型的嵌套 §

• 如果为多层嵌套，其内部所嵌套的每层声明应当用field进行初始化，否则会导致声明指向同一变量（Python stores default member variable values in class attributes.）， 参考
  • 正确示例 输出为1和2

  from dataclasses import dataclass, field
   
  ## inner most data
  @dataclass
  class Lv0:
      x: float=0
  ## the structure in the middle
  @dataclass
  class Lv1:
      y0: Lv0 = field(default_factory=lambda: Lv0()) # not y0: Lv0 = Lv0()
   
  ## outer most data
  @dataclass
  class Lv2:
      z0: Lv1 = field(default_factory=lambda: Lv1())
   
  if __name__ == '__main__':
      a = Lv2()
      b = Lv2()
      a.z0.y0.x = 1
      b.z0.y0.x = 2
      print(a.z0.y0.x) ## get 1
      print(b.z0.y0.x) ## get 2

  • 错误示例，a和b的.z0.y0指向了同一变量，输出为2和2

  from dataclasses import dataclass, field
   
  @dataclass
  class Lv0:
      x: float=0
   
  @dataclass
  class Lv1:
      y0: Lv0 = Lv0()
   
  @dataclass
  class Lv2:
      z0: Lv1 = field(default_factory=lambda: Lv1())
   
  if __name__ == '__main__':
      a = Lv2()
      b = Lv2()
      a.z0.y0.x = 1
      b.z0.y0.x = 2
      print(a.z0.y0.x) ## get 2
      print(b.z0.y0.x) ## get 2