__new__ on abstract classes produces false positive "Cannot instantiate abstract class"
Nobody has claimed this yet.
- Dominant language
- Python
- Stars
- 20.6k
- Forks
- 3.3k
- PR merge metrics
- PR metrics pending
Description
Bug Report
When an abstract class defines __new__ (note, not __init__) method, mypy produces error when that class is instantiated, even though __new__() does not imply instantiation.
To Reproduce
from abc import ABCMeta, abstractmethod
class Abstract(metaclass=ABCMeta):
def __new__(cls) -> "Abstract":
return super().__new__(Concrete)
@abstractmethod
def hello(self) -> int:
...
class Concrete(Abstract):
def hello(self) -> int:
return 0
x = Abstract()
print(x.hello())
Expected Behavior
No errors reported when checked with mypy. Calling a class with __new__ method shuld be effectively treated as just calling a simple method, like
def make_abstract() -> "Abstract":
return Concrete()
Actual Behavior
error message is printed:
error: Cannot instantiate abstract class "Abstract" with abstract attribute "hello" [abstract]
Your Environment
- Mypy version used: mypy-0.991
- Mypy command-line flags: none
- Mypy configuration options from
mypy.ini(and other config files): none - Python version used: 3.10.6
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
No repository file or test is named in the issue. Start with the supplied Python reproducer and trace mypy's abstract-class instantiation check when new is defined; done means the false [abstract] error is absent while the intended abstract-class diagnostic remains covered by a regression test.
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