functools.update_wrapper() will not accept descriptor (decorator) as wrapper
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Description
Description:
The type stub for functools.update_wrapper() does not permit a descriptor for the wrapper (first) argument, a legitimate case arising when defining a descriptor-type decorator (like @property is).
https://github.com/python/typeshed/blob/main/stdlib/functools.pyi#L83
@erictraut While perhaps not exactly a regression, this used to work up until this commit of yours here (last week): https://github.com/python/typeshed/commit/9c4bfd5d11b47677e128452baa8ac7eeb1903a8e#diff-02c51ed45b741b6765c365fb5d6578c586510bbbd57b10a1dba10aeba37ae157L70-R84. I say not exactly a regression because the prior constraint introduced here was perhaps overly loose: https://github.com/python/typeshed/pull/4627/files
Example
As an example, the following (pyright) typing error is detected in the lazyproperty descriptor-type decorator defined here: https://gist.github.com/scanny/255f16339b74b2b59e896d67bd459d6b
lazyproperty.py|65 col 34-38 error| Argument of type "Self@lazyproperty[T@lazyproperty]"
cannot be assigned to parameter "wrapper"
of type "(**_PWrapper@update_wrapper) -> _RWapper@update_wrapper"
in function "update_wrapper"
Type "Self@lazyproperty[T@lazyproperty]" cannot be assigned to
type "(**_PWrapper@update_wrapper) -> _RWapper@update_wrapper"
To Reproduce
The gist referenced above has no dependencies other than the stdlib so can be type-checked directly (using pyright v1.1.296):
$ pyright lazyproperty.py
Analysis
The type definition at work constrains wrapper to be a Callable[_PWrapper, _RWapper]. I believe it also needs to permit Descriptor, although I'm not completely sure what that type definition is. My best guess is something like this:
class HasDunderGet(Protocol):
def __get__(self, obj: Any, type: type = None) -> Any: ...
class HasDunderSet(Protocol):
def __set__(self, obj: Any, value: Any) -> None: ...
class HasDunderDelete(Protocol):
def __delete__(self, obj: Any) -> None: ...
Descriptor = Union[HasDunderGet, HasDunderSet, HasDunderDelete]
Expected behavior
As far as I can tell, this is a legitimate usage of functools.update_wrapper() and decorators that produce a descriptor (like @property does) are also legitimate Python. It has certainly worked for a long time and also even typechecked with pyright previously (v1.1.273), maybe six months ago. So I would expect it to be accepted as written.
Contributor guide
First steps
- Read the whole issue, then the project's contributing guide.
- Comment on the issue to say you are picking it up — it saves two people doing the same work.
- Fork the repository and make your change on a branch.
- Open a pull request that references the issue number.
Research direction
Start with stdlib/functools.pyi around lines 82-87 and compare the wrapper annotation with the descriptor use in the linked lazyproperty.py gist. Run pyright v1.1.296 on lazyproperty.py to reproduce the error, then inspect the referenced typeshed commit and earlier pull request for context. Done means the legitimate descriptor decorator type-checks without weakening unrelated update_wrapper typing.
Written by the indexing model from the issue text.
Assessment
- Tech stack
- python
- Domain
- developer-experience, tooling
- Issue type
- Bug
- Difficulty
- 4/5
- Estimated time
- 3-5 days
- Activity status
- Stale
- Clarity
- Mostly clear
- Newbie friendliness
- 35/100