Unjustified(?) unbound var warning in try exception statements

[abelcheung]

Environment data

• Language Server version: 2021.2.0 or newer
• OS and version: XXX
• Python version (& distribution if applicable, e.g. Anaconda): XXX

Issue

Code sample below would cause Pylance to issue type check error, please see screenshot further down. I think this is a regression, since Pylance 2021.1.3 passes checking for this code snippet.

Code Sample

try:
    # any statement will do
    _ = 'text'.index('a')
except:
    var = 1
else:
    var = 2
finally:
    print(var)

Screenshot

[erictraut]

I agree this is a false positive error. It arises from a fix for another class of false positives that previously occurred with try/except/else/finally statements.

In this very specific case, where there is both an "else" clause and a "bare except" clause (i.e. an except clause with no specified exception type) and a finally clause, we can avoid this particular false positive. I'll make the change to fix this specific case. I'll point out that if you add an exception type to the except clause (e.g. except NameError:), then this is a legitimate error because an exception of a different type could directly execute the finally clause.

[abelcheung]

Indeed you're correct about the other non-corner cases. Thanks for the prompt triaging!

[erictraut]

This will be fixed in the next release of pylance.

Here's the PR in case you're interested: microsoft/pyright@5bf5640. I used your sample in the unit test. :)

Thanks for the bug report.

[jakebailey]

This issue has been fixed in version 2021.2.1, which we've just released. You can find the changelog here: https://github.com/microsoft/pylance-release/blob/main/CHANGELOG.md#202121-10-february-2021