Pylance isinstance bug ?

[pasunx]

Environment data

• Language Server version: 2021.6.3
• OS and version: win32 x64
• Python version (and distribution if applicable, e.g. Anaconda):
• python.analysis.indexing: undefined
• python.analysis.typeCheckingMode: strict

from typing import Any

class AST: ...

class Foo(AST):

    value: str

class Bar(AST):

    value: AST

def handler(node: AST) -> Any:
    if isinstance(node, Foo):
        return node.value
    elif isinstance(node, Bar):
        if isinstance(node.value, Foo): # Unnecessary isinstance call; "str" is never an instance of "Foo" Pylance(reportUnnecessaryIsInstance)
            return node.value

this also.

class Baz(AST):

    value: str

class Qux(AST):

    value: int

def handler(node: AST) -> Any:
    if isinstance(node, Baz):
        result = [node.value] # type: list[str] # Expression of type "list[str]" cannot be assigned to declared type "list[int]"
                                                #  TypeVar "_T@list" is invariant
                                                #    "str" is incompatible with "int"
        return result
    elif isinstance(node, Qux):
        result = [node.value] # type: list[int]
        return result

[erictraut]

Thanks for the bug report. This will be fixed in the next release.

[jakebailey]

This issue has been fixed in version 2021.7.0, which we've just released. You can find the changelog here: https://github.com/microsoft/pylance-release/blob/main/CHANGELOG.md#202170-6-july-2021