形窄联

Question

如何按形状缩小联合体？我不想用isinstance或手动转换来检查实际类型（有很多类型）

class X:
    title = "1"
class Y:
    name = "2"
class Z:
    name = "3"

for (i, r) in enumerate([X(), Y(), Z()]): # type of r: X | Y | Z

    if hasattr(r, "title"):
        print(r.title) # error
    else:
        print(r.name)  # error

类型检查错误显示：

(variable) title: str | Unknown
Cannot access member "title" for type "Y"
  Member "title" is unknown
Cannot access member "title" for type "Z"
  Member "title" is unknown

(variable) name: Unknown | str
Cannot access member "name" for type "X"
  Member "name" is unknown

Answer 1

在您的案例中，有几种方法可以欺骗Pylance检查器：

class X:
    title = "1"
class Y:
    name = "2"
class Z:
    name = "3"

for (i, r) in enumerate([X(), Y(), Z()]): # type of r: X | Y | Z

    if hasattr(r, "title"):
        print(r.title) # type: ignore
    else:
        print(r.name) # type: ignore

class X:
    title = "1"
class Y:
    name = "2"
class Z:
    name = "3"

for (i, r) in enumerate([X(), Y(), Z()]): # type of r: X | Y | Z

    if hasattr(r, "title"):
        print(getattr(r, "title"))
    else:
        print(getattr(r, "name"))