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Type guard in list comprehension with assignment expression does not constrain type #8236
Description
- Are you reporting a bug, or opening a feature request? Bug
from typing import List, Iterator
import os
import re
def get_schema_versions(self) -> List[int]:
return [int(match.group(0))
for filename in os.listdir('schema')
if (match := re.fullmatch(r'(\d+)\.sql', filename)) is not None]
def get_schema_versions2(self) -> Iterator[int]:
for filename in os.listdir('schema'):
match = re.fullmatch(r'(\d+)\.sql', filename)
if match is not None:
yield int(match.group(0))- What is the actual behavior/output?
In the first function, mypy interprets the match variable as Optional[Match[str]] and flags the use of the possibly-None object. In the second function, match under the if statement is considered Match[str].
- What is the behavior/output you expect?
Since both statements guard the match variable against being None, both uses should be of type Match[str].
- What are the versions of mypy and Python you are using? mypy 0.761, Python 3.8
Do you see the same issue after installing mypy from Git master? Don't know how - What are the mypy flags you are using? (For example --strict-optional) Nothing relevant
Activity
fluggo commentedon Jan 6, 2020
This might be the same bug as #7316.
Narrow types for walrus in identity comparison
Narrow types for walrus in identity comparison
msullivan commentedon Feb 28, 2020
Closing in favor its duplicate #8447 which is about to be fixed anyway
hauntsaninja commentedon Sep 27, 2020
@fluggo I was wondering if the code you're working on is open source? My interest is in adding projects to https://github.com/hauntsaninja/mypy_primer that use newer Python features.
fluggo commentedon Sep 28, 2020
@hauntsaninja Sorry, this project wasn't. I appreciate the ask, though.