CODEWITHSUNDEEP
pythonpython-typing
Scott Stafford
Scott Stafford

Reputation: 44818

How do you type-hint class prototypes that don't otherwise exist?

I have legacy code with inheriting dataclasses:

@dataclass
class Base:
    a: int

@dataclass
class Derived1(Base):
    b: int

@dataclass
class Derived2(Base):
    b: int

I want to use Python type hints so that methods know when they're getting something with a b attribute. However, I cannot import actual Derived1 or Derived2. So I want something like:

def uses_b(b_supporting_object: TIsBaseWithB):
    ...

How do you define a TIsBaseWithB? Is NewType related?

Upvotes: 0

Views: 315

Answers (1)

Paweł Rubin
Paweł Rubin

Reputation: 3439

Use typing.Protocol:

from typing import Protocol


class SupportsB(Protocol):
    b: int

Upvotes: 1

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