来自父类的提示

Question

How can you hint a class from the parent class like this?

class Cls1:
    class Cls2:
        p2: int

    class Cls3:
        p3: Cls2  # undefined name 'Cls2'

    class Cls4:
        p4: Cls2  # undefined name 'Cls2'

Answer 1

Yes, see PEP 484 §Forward References :

When a type hint contains names that have not been defined yet, that definition may be expressed as a string literal, to be resolved later.

A situation where this occurs commonly is the definition of a container class, where the class being defined occurs in the signature of some of the methods.

So, in your example, reference the not-yet-defined type in a string:

class Cls1:
    class Cls2:
        p2: int

    class Cls3:
        p3: 'Cls2'

    class Cls4:
        p4: 'Cls2'

Note that, while Python is happy to accept the above, mypy (v0.641), seems to have a bug and can't find Cls2 .