`self.__class__` produces a type check with a constructor where a concrete reference to the class works fine
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Description
Bug Report
I'm not sure how this bug generalizes, but I discovered this with an HTTP headers abstraction with a clone method and the example minifies pretty far down, as shown below
To Reproduce
from typing import Mapping, Sequence, AnyStr, Self
class c:
_v: dict[bytes, list[bytes]]
def __init__(self, v: Mapping[AnyStr, Sequence[AnyStr]]):
pass
def clonecls(self) -> Self:
return self.__class__(self._v)
def clone(self) -> c:
return c(self._v)
https://mypy-play.net/?mypy=latest&python=3.12&gist=0be4308fb57a3685fafab2ac51a97c85
Expected Behavior
No errors.
Actual Behavior
main.py:9: error: Argument 1 to "c" has incompatible type "dict[bytes, list[bytes]]"; expected "Mapping[AnyStr, Sequence[AnyStr]]" [arg-type]
Your Environment
- Mypy version used: 1.13.0
- Mypy command-line flags: none
- Mypy configuration options from
mypy.ini(and other config files): none - Python version used: 3.12
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 the minimal reproducer in main.py or the linked mypy-play example, comparing clonecls() using self.class with clone() using c directly. Run mypy with the reported Python 3.12 setup and add a regression test that captures the expected absence of an argument-type error.
Written by the indexing model from the issue text.
Assessment
- Tech stack
- python
- Domain
- devtools
- Issue type
- Bug
- Difficulty
- 4/5
- Estimated time
- 3-5 days
- Activity status
- Stale
- Clarity
- Mostly clear
- Newbie friendliness
- 35/100