Fix decorator in retry module

[fperrin]

Hi,

I'm afraid the type annotations for the retry module are incorrect, although it's possible that the real issue is in mypy; it's possible I don't understand typing annotations enough to be 100% sure.

I want to typecheck the following program with mypy:

from retry import retry

@retry(tries=5)
def foo(bar: str) -> int: ...

# Valid code
bar: int
bar = foo("abc")

# Should fail (twice): both argument and return value have incompatible types
baz: dict
baz = foo([])

reveal_type(retry)

Running with python3.7 (as provided by Debian) or 3.9.4 (latest version compiled locally) with mypy 0.820 and types-retry 0.1.1, I get the following:

% mypy demo.py
demo.py:3: error: Argument 1 has incompatible type "Callable[[str], int]"; expected <nothing>
demo.py:8: error: <nothing> not callable
demo.py:12: error: <nothing> not callable
demo.py:14: note: Revealed type is "def [_T <: def (*Any, **Any) -> Any] (exceptions: Union[Type[builtins.Exception], builtins.tuple[Type[builtins.Exception]]] =, tries: builtins.int =, delay: builtins.float =, max_delay: Union[builtins.float, None] =, backoff: builtins.float =, jitter: Union[Tuple[builtins.float, builtins.float], builtins.float] =, logger: Union[logging.Logger, None] =) -> def (_T`-1) -> _T`-1"
Found 3 errors in 1 file (checked 1 source file)

Which is not right.

With the changes included in this PR, I get the expected errors from mypy:

% env MYPYPATH=$PWD/stubs/retry mypy demo.py
demo.py:12: error: Incompatible types in assignment (expression has type "int", variable has type "Dict[Any, Any]")
demo.py:12: error: Argument 1 to "foo" has incompatible type "List[<nothing>]"; expected "str"
demo.py:14: note: Revealed type is "def (exceptions: Union[Type[builtins.Exception], builtins.tuple[Type[builtins.Exception]]] =, tries: builtins.int =, delay: builtins.float =, max_delay: Union[builtins.float, None] =, backoff: builtins.float =, jitter: Union[Tuple[builtins.float, builtins.float], builtins.float] =, logger: Union[logging.Logger, None] =) -> retry.api._Decorator"
Found 2 errors in 1 file (checked 1 source file)

I copied the definition of _Decorator from stubs/click/click/decorators.pyi.

[hauntsaninja]

Thanks, this looks good to me.

For the record, I think this might be a bug in mypy, since:

diff --git a/stubs/retry/retry/api.pyi b/stubs/retry/retry/api.pyi
index 88f274b9..6e1a0edd 100644
--- a/stubs/retry/retry/api.pyi
+++ b/stubs/retry/retry/api.pyi
@@ -25,4 +25,4 @@ def retry(
     backoff: float = ...,
     jitter: Union[Tuple[float, float], float] = ...,
     logger: Optional[Logger] = ...,
-) -> _Decorator[_T]: ...
+) -> Callable[[_T], _T]: ...

is also enough to fix.

However, IIRC this shorthand where the TypeVar only occurs in the return type is sort of contentious syntax between type checkers, so using the callback protocol is probably for the best.

[hauntsaninja]

Dug up the thread: https://mail.python.org/archives/list/typing-sig@python.org/thread/DDR2B3USYCQGVXM3ZSK2FASH5YFQGPUV/

[srittau]

I extracted IdentityFunction to _typeshed in #5483, like I said we should. We can use that in this PR.

[fperrin]

Thanks for having a look @hauntsaninja .
@srittau , should I wait for #5483 to be merged and update this PR? Or you want to make the change to retry yourself?

[srittau]

Whatever you prefer, I can do it, or you can wait.

[fperrin]

Finish your work on 5483, I'll take care of retry later.

[srittau]

#5483 is merged now.

[fperrin]

Merged master and updated to use IdentifyFunction.

[fperrin]

Thanks @srittau & @hauntsaninja !