Problems with overloads / mypy bug

[thepabloaguilar]

I'm having some errors with typing, if it's not a returns problem feel free to close this issue

Mypy errors:

get_stream_details.py:78: error: Argument 1 to "apply" of "Result" has incompatible type "Result[overloaded function, Any]"; expected "Result[Callable[[Stream], StreamDetails], FailureDetails]"
get_stream_details.py:78: error: Argument 1 has incompatible type "Result[StreamDetails, FailureDetails]"; expected "Maybe[Any]"
get_stream_details.py:78: error: Incompatible return value type (got "Maybe[Any]", expected "Result[StreamDetails, FailureDetails]")
get_stream_details.py:79: error: Argument 1 to "_flow" has incompatible type "Result[overloaded function, Any]"; expected "Result[overloaded function, Any]"
get_stream_details.py:79: error: Argument 1 to "from_value" of "Result" has incompatible type overloaded function; expected overloaded function
get_stream_details.py:81: error: Cannot infer type argument 1 of "_bind"
get_stream_details.py:81: error: Argument 1 to "_bind" has incompatible type "Callable[[Any], Result[Any, FailureDetails]]"; expected "Callable[[Any], Maybe[Any]]"
get_stream_details.py:81: error: Incompatible return value type (got "Result[Any, FailureDetails]", expected "Maybe[object]")
get_stream_details.py:81: error: Incompatible return value type (got "Result[Any, FailureDetails]", expected "Maybe[Any]")
get_stream_details.py:81: error: Cannot infer type argument 1 of "Success"
get_stream_details.py:82: error: Cannot infer type argument 1 of "_bind"
get_stream_details.py:82: error: Argument 1 to "_bind" has incompatible type "Callable[[Any], Result[Any, FailureDetails]]"; expected "Callable[[Any], Maybe[Any]]"
get_stream_details.py:82: error: Incompatible return value type (got "Result[Any, FailureDetails]", expected "Maybe[object]")
get_stream_details.py:82: error: Incompatible return value type (got "Result[Any, FailureDetails]", expected "Maybe[Any]")
get_stream_details.py:82: error: Cannot infer type argument 1 of "Success"

All the errors above are from my return statement in GetStreamDetailsUsecase.__call__!

Code:

@dataclass_json
@dataclass
class StreamDetails:
    stream: Stream
    projects: List[Project]
    ksql_stream_detailed: KSQLStreamDetailed

    @classmethod
    @curry
    def build(
        cls,
        stream: Stream,
        projects: List[Project],
        ksql_stream_detailed: KSQLStreamDetailed,
    ) -> "StreamDetails":
        return cls(stream, projects, ksql_stream_detailed)


class FindStreamByStreamId(ABC):
    @abstractmethod
    def __call__(self, stream_id: UUID) -> Result[Maybe[Stream], FailureDetails]:
        pass


class FindProjectsByStream(ABC):
    @abstractmethod
    def __call__(self, stream: Stream) -> Result[List[Project], FailureDetails]:
        pass


# "GetStreamByNameUsecase" definition
# class GetStreamByNameUsecase:
#     def __call__(
#             self, stream_name: str
#         ) -> Result[KSQLStreamDetailed, BusinessFailureDetails]:
#         pass


class GetStreamDetailsUsecase:
    def __init__(
        self,
        find_stream_by_stream_id: FindStreamByStreamId,
        find_projects_by_stream: FindProjectsByStream,
        get_stream_by_name: GetStreamByNameUsecase,
    ):
        self.__find_stream_by_stream_id = find_stream_by_stream_id
        self.__find_projects_by_stream = find_projects_by_stream
        self.__get_stream_by_name = get_stream_by_name

    def __call__(self, stream_id: UUID) -> Result[StreamDetails, FailureDetails]:
        stream = self.__find_stream_by_stream_id(stream_id).bind(
            self.__verify_if_stream_exist
        )
        partial_projects = partial(stream.bind, self.__find_projects_by_stream)
        partial_ksql = partial(
            stream.bind, lambda stream_: self.__get_stream_by_name(stream_.name)
        )

        return flow(
            Result.from_value(StreamDetails.build),
            stream.apply,
            bind(lambda to_apply: partial_projects().apply(Success(to_apply))),
            bind(lambda to_apply: partial_ksql().apply(Success(to_apply))),
        )

    def __verify_if_stream_exist(
        self, stream: Maybe[Stream]
    ) -> Result[Stream, BusinessFailureDetails]:
        return maybe_to_result(stream).alt(
            lambda __: BusinessFailureDetails(
                reason="NOT_FOUND", failure_message="Stream not found"
            )
        )

---

But if I change the flow to handmade flow just one error appeared:

Mypy error:

error: Argument 1 to "from_value" of "Result" has incompatible type overloaded function; expected overloaded function

Code:

class GetStreamDetailsUsecase:
    # CODE

    def __call__(self, stream_id: UUID) -> Result[StreamDetails, FailureDetails]:
        stream = self.__find_stream_by_stream_id(stream_id).bind(
            self.__verify_if_stream_exist
        )
        partial_projects = partial(stream.bind, self.__find_projects_by_stream)
        partial_ksql = partial(
            stream.bind, lambda stream_: self.__get_stream_by_name(stream_.name)
        )

        details = Result.from_value(StreamDetails.build)
        details_added_stream = stream.apply(details)
        details_added_projects = details_added_stream.bind(lambda to_apply: partial_projects().apply(Success(to_apply)))
        details_added_ksql = details_added_projects.bind(lambda to_apply: partial_ksql().apply(Success(to_apply)))
        return details_added_ksql

    # CODE

[sobolevn]

Ok, looks like we found a bug in mypy. Here's the minimal example that works:

from returns.curry import curry
from returns.result import Result

@curry
def first(a: int, b: int) -> int:
    ...

reveal_type(
    Result.from_value(first),
)
# Revealed type is 'returns.result.Result[Overload(def (a: builtins.int) -> def (b: builtins.int) -> builtins.int, def (a: builtins.int, b: builtins.int) -> builtins.int), Any]'

But, this does not:

from returns.curry import curry
from returns.result import Result

@curry
def first(a: int, b: int, c: int) -> int:
    ...

reveal_type(
    Result.from_value(first),
)

Output:

» mypy ex.py
ex.py:9: note: Revealed type is 'returns.result.Result[Overload(def (a: builtins.int) -> Overload(def (b: builtins.int, c: builtins.int) -> builtins.int, def (b: builtins.int) -> def (c: builtins.int) -> builtins.int), def (a: builtins.int, b: builtins.int) -> def (c: builtins.int) -> builtins.int, def (a: builtins.int, b: builtins.int, c: builtins.int) -> builtins.int), Any]'
ex.py:9: error: Argument 1 to "from_value" of "Result" has incompatible type overloaded function; expected overloaded function
Found 1 error in 1 file (checked 1 source file)

Can you please create a new bug in mypy's issue tracker?

[sobolevn]

Minimal reproduction: https://github.com/sobolevn/mypy-bug-410
mypy issue: python/mypy#9017

[sobolevn]

Sorry, I haven't seen python/mypy#8978
I have closed my new issue as a duplicate.

[thepabloaguilar]

Waiting for your changes to be released and finally close this issue!!