Non existing member does not get reported when using +=, -=,... operators

[meollab]

Environment data

• Language Server version: 2021.9.2
• OS and version: Linux x64
• Python version (and distribution if applicable, e.g. Anaconda): Python 3.7.5 (64bit)
• python.analysis.indexing: undefined
• python.analysis.typeCheckingMode: basic

Expected behaviour

class ExampleA:
    def blah(self) -> None:
        self.does_not_exist_a += 3

should report does_not_exist_a as not existing

Actual behaviour

Pyright does not report any error or warning

Code Snippet / Additional information

• The problem with does_not_exist_a is reported by both mypy and pylint
  • mypy: error: "ExampleA" has no attribute "does_not_exist_a"
  • pylint: E1101: Instance of 'ExampleA' has no 'does_not_exist_a' member (no-member)
• Pyright correctly reports Cannot access member "does_not_exist_b" for type "ExampleB"  Member "does_not_exist_b" is unknown here

class ExampleB:
    def blah(self) -> None:
        print(self.does_not_exist_b)

[erictraut]

Thanks for the bug report. I agree that this is a false negative case that a static type checker can detect. In particular, if the only assignments to an instance variable are through augmented assignment expressions, it should be flagged as an error.

[erictraut]

This will be addressed in the next release.

[jakebailey]

This issue has been fixed in version 2021.9.3, which we've just released. You can find the changelog here: https://github.com/microsoft/pylance-release/blob/main/CHANGELOG.md#202193-22-september-2021