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pythonpython-typingmypy
Pawel
Pawel

Reputation: 393

Signature of {method} incompatible with super type {Class}

While trying to update my code to be PEP-484 compliant (I'm using mypy 0.610) I've ran into the following report:

$ mypy mymodule --strict-optional --ignore-missing-imports --disallow-untyped-calls --python-version 3.6

myfile.py:154: error: Signature of "deliver" incompatible with supertype "MyClass"

MyClass:

from abc import abstractmethod

from typing import Any


class MyClass(object):

    @abstractmethod
    def deliver(self, *args: Any, **kwargs: Any) -> bool:
        raise NotImplementedError

myfile.py:

class MyImplementation(MyClass):

[...]

    def deliver(self, source_path: str,
                dest_branches: list,
                commit_msg: str = None,
                exclude_files: list = None) -> bool:

        [...]

        return True

I'm definitely doing something wrong here, but I can't quite understand what

Any pointers would be much appreciated.

Upvotes: 23

Views: 20569

Answers (3)

tasuren
tasuren

Reputation: 319

You can solve the question by using Callable[..., Any] and type: ignore such like bellow.

from typing import Callable

class MyClass(object):
    deliver: Callable[..., bool]
    @abstractmethod
    def deliver(self, *args, **kwargs): # type: ignore
        raise NotImplementedError

Upvotes: -3

Andrey Semakin
Andrey Semakin

Reputation: 2795

Maybe you should work it around this way:

  1. Define abstract method without arguments:

    class MyClass:
    @abstractmethod
    def deliver(self) -> bool:
        raise NotImplementedError

  2. In implementations get all your data from self:

    class MyImplementation(MyClass):
    def __init__(
            self,
            source_path: str,
            dest_branches: list,
            commit_msg: str = None,
            exclude_files: list = None
    ) -> None:
        super().__init__()
        self.source_path = source_path
        self.dest_branches = dest_branches
        self.commit_msg = commit_msg
        self.exclude_files = exclude_files

    def deliver(self) -> bool:
        # some logic
        if self.source_path and self.commit_msg:
            return True
        return False

This way you will have completely compatible method declarations and still can implement methods as you want.

Upvotes: -3

user2357112
user2357112

Reputation: 281842

@abstractmethod
def deliver(self, *args: Any, **kwargs: Any) -> bool:
    raise NotImplementedError

This declaration doesn't mean subclasses can give deliver any signature they want. Subclass deliver methods must be ready to accept any arguments the superclass deliver method would accept, so your subclass deliver has to be ready to accept arbitrary positional or keyword arguments:

# omitting annotations
def deliver(self, *args, **kwargs):
    ...

Your subclass's deliver does not have that signature.

If all subclasses are supposed to have the same deliver signature you've written for MyImplementation, then you should give MyClass.deliver the same signature too. If your subclasses are going to have different deliver signatures, maybe this method shouldn't really be in the superclass, or maybe you need to rethink your class hierarchy, or give them the same signature.

Upvotes: 23

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