Pylance reports reportUnboundVariable when using walrus operator with conditional expressions and no brackets

[charles-dexter-ward]

Environment data

• Language Server version: 2020.9.5
• OS and version: Windows 10
• Python version: 3.8.5

Expected behaviour

The following snippet leads to a reportUnboundVariable on the items variable used in the for statement

 if items := result.get("Items", None) if result else None:
    for item in items:
        pass

The following snippets do not generate any reports

 if items := (result.get("Items", None) if result else None):
    for item in items:
        pass

 if items := result.get("Items", None):
    for item in items:
        pass

Actual behaviour

Usiing the walrus operator with a conditional expression which is not enclosed in parentheses leads to a reportUnboundVariable report

Code Snippet / Additional information

[erictraut]

Thanks for the bug report.

When I initially added support for the walrus operator, I based my implementation on the draft specification. It appears that there was a change in the final specification that made it legal to use a ternary expression (X if Y else Z) in the right-hand side of the walrus operator.

I've updated the code to support the final spec, and the fix will be in the next version of Pylance.

[jakebailey]

This issue has been fixed in version 2020.9.6, which we've just released. You can find the changelog here: https://github.com/microsoft/pylance-release/blob/master/CHANGELOG.md#202096-23-september-2020