CODEWITHSUNDEEP
pythontype-hinting
raduw
raduw

Reputation: 1098

(Python type hints) How to specify type being currently defined as the returned type from a method?

I would like to specify (as a type hint) the currently defined type as the return type from a method.

Here's an example:

class Action(Enum):
    ignore = 0
    replace = 1
    delete = 2

    @classmethod
    # I would like something like
    # def idToObj(cls, elmId: int)->Action:
    # but I cannot specify Action as the return type
    # since it would generate the error
    # NameError: name 'Action' is not defined
    def idToObj(cls, elmId: int):
        if not hasattr(cls, '_idToObjDict'):
            cls._idToObjDict = {}
            for elm in list(cls):
                cls._idToObjDict[elm.value] = elm

        return cls._idToObjDict[elmId]

Ideally I would have liked to specify something like

def idToObj(cls, elmId: int)->Action:

Thank you.

Upvotes: 2

Views: 123

Answers (1)

Łukasz Rogalski
Łukasz Rogalski

Reputation: 23243

This case is mentioned in official type hints PEP:

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.

class Tree:
    def __init__(self, left: Tree, right: Tree):
        self.left = left
        self.right = right

To address this, we write:

class Tree:
    def __init__(self, left: 'Tree', right: 'Tree'):
        self.left = left
        self.right = right

In your case It would be:

def idToObj(cls, elmId: int)->'Action':
    pass  # classmethod body

Upvotes: 5

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