Unpacking multiple iterables yields false negatives

[derhintze]

Environment data

• Language Server version: 2022.2.1 (pyright 618f54ed)
• OS and version: Red Hat 4.8.5-44
• Python version (& distribution if applicable, e.g. Anaconda): Python 3.9.1

Expected behaviour

To not flag anything as wrong.

Actual behaviour

Multiple errors errors found:

• Expected expression
• Expected ":"
• Only one unpack operation allowed in list

Logs

(25626) Background analysis message: setFileOpened
(25626) Background analysis message: getDiagnosticsForRange
(25626) Background analysis message: getDiagnosticsForRange
(25626) Background analysis message: getSemanticTokens full
(25626) [BG(1)] getSemanticTokens full at /radarugs/hintze/s4-cnc-tools/test.py (5ms)
(25626) Background analysis message: analyze

Code Snippet / Additional information

The following executes w/o problems in Python:

a = [1, 2]
b = ["3", "4"]

for x in *a, *b:
    print(x)

c = *a, *b
print(c)

Yields the following output:

1
2
3
4
(1, 2, '3', '4')

But pylance marks the first * in line 4 (the for-loop) with Expected expression, the colon in the same line as Expected ":", and the second unpacking in line 7 (where c is assigned) as Only one unpack operation allowed in list.

This is probably (partly?) related to #700.

[derhintze]

Black also doesn't understand this expression: psf/black#2878

[derhintze]

also note that this syntax is only valid for Python >= 3.9

[erictraut]

Thanks for the bug report. I wasn't aware of this change to the grammar in Python 3.9. Since this is a core type checker issue, I've created a tracking bug in the pyright repo. microsoft/pyright#3029

[erictraut]

This will be fixed in the next release.

[debonte]

This issue has been fixed in version 2022.2.3, which we've just released. You can find the changelog here: CHANGELOG.md

[realworldhacker]

expected expression error in visual studio code from an elif statement I tried to run. parenthesis only fixed if statement error, I', finding a hard time finding a solution for my current problem. following a PyCharm tutorial btw; but I'm having a hard time downloading it. https://www.youtube.com/watch?v=0fC1JsN8AsM 39:42

[debonte]

@realworldhacker, I copied the code from that spot in the video (see below) and Pylance doesn't show any errors for me, so I'm assuming you have a typo somewhere in the code. One wild guess is that you typed elif instead of else on the second to last line.

If you believe that there is a problem with Pylance here, please open a new issue and include a minimal code snippet that reproduces the problem.

fnum = input("What is the first number ")
snum = input("What is the second number")

if fnum > snum:
    print("The first number is larger!")
elif snum > fnum:
    print("The second number is larger. ")
else:
    print("The numbers are the same")