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Unexpected error when inheriting a class from Popen and overriding some method in it #7597
Description
-
Are you reporting a bug, or opening a feature request?
Bug -
Please insert below the code you are checking with mypy,
or a mock-up repro if the source is private. We would appreciate
if you try to simplify your case to a minimal repro.
import subprocess
from typing import List, Tuple
class MyPopen(subprocess.Popen):
def communicate(self, _input=None, _timeout=None) -> Tuple[bytes, bytes]:
return super().communicate(_input, _timeout)
def interactive_spawn(cmd: List[str], **kwargs) -> MyPopen:
process = MyPopen(cmd, **kwargs)
process.communicate()
return process- What is the actual behavior/output?
$ mypy mypy_subprocess.py mypy_subprocess.py:13: error: Incompatible return value type (got "Popen[Any]", expected "MyPopen") Found 1 error in 1 file (checked 1 source file)
- What is the behavior/output you expect?
$ mypy mypy_subprocess.py Success: no issues found in 1 source file
- What are the versions of mypy and Python you are using?
Do you see the same issue after installing mypy from Git master?
$ mypy --version mypy 0.730
(env) $ mypy --version mypy 0.740+dev.583b99e5096c979043a63dcf92bf3f0d5993d03a
NOTE: it's not reproducing with 0.720
$ python --version Python 3.7.4
- What are the mypy flags you are using? (For example --strict-optional)
- If mypy crashed with a traceback, please paste
the full traceback below.
Activity
msullivan commented on Oct 2, 2019
Yeah this got introduced in 0.730. I need to spend some time tweaking the rules for __new__ return types maybe.
Only return a declared type from __new__ if it is a subtype of the class
Only return a declared type from __new__ if it is a subtype of the cl…