Incorrect reportOptionalSubscript when accessing List with checked length.

[NielsKorschinsky]

Environment data

• Language Server version: 2022.7.30
• OS and version: win32 x64
• Python version (and distribution if applicable, e.g. Anaconda):
• python.analysis.indexing: null
• python.analysis.typeCheckingMode: strict

Code Snippet

group_tags: Optional[List[str]] = ["hello", "\"anotherVal\""]
tag_dict: Optional[Dict[str, str]] = {"hello": "wantedId", "anotherVal": "wantedName"}
insert_tags: Dict[str, Optional[str]] = {}

if group_tags and tag_dict:
    if "something" in group_tags:
        pass
    else:
        insert_tags["id_value"] = tag_dict[group_tags[0].replace("\"", "")]
        if len(group_tags) > 1:
            insert_tags["name_value"] = tag_dict[group_tags[1].replace("\"", "")]

Error on the part group_tags (last line, accessing [1])

(parameter) group_tags: List[str]
Object of type "None" is not subscriptablePylance[reportOptionalSubscript](https://github.com/microsoft/pylance-release/blob/main/DIAGNOSTIC_SEVERITY_RULES.md#diagnostic-severity-rules)

Logs

I will add it if requested.

This setting cannot be applied in this workspace. It will be applied when you open the containing workspace folder directly.

[NielsKorschinsky]

Deleting the replace removes this bug, though the marker is only on the group_tags-part.

[erictraut]

I'm not able to repro the problem you're seeing. Can you please verify that the above code snippet is correct? It contains a bug on the second line. Even if I fix that bug, I don't see any errors reported by pylance.

[NielsKorschinsky]

I just copy pasted the segment.
I only added the first three lines to show off the variable declaration.

Copied again from the linting:
insert_tags: Dict[str, Optional[str]]
tag_dict: Dict[str, str] | None
group_tags: List[str] | None

[NielsKorschinsky]

I have fixed the error in line 2 now, please try again to reproduce.

[erictraut]

To confirm, you're able to see the error with the self-contained minimal code sample above? I don't see any error with this code. Please try pasting this code into its own ".py" file and make sure you can repro the problem there. If you can, we'll need to figure out what's different between your configuration and mine.

[NielsKorschinsky]

I tried and I am not able to reproduce either.
I need to add a tuple-unpacking in a loop to reproduce it.

I cannot attach the file, therefore here is the full code 1-1:

from typing import Optional, List, Dict, Tuple, Any

group_tags: Optional[List[str]] = ["hello", "\"anotherVal\""]
insert_tags: Dict[str, Optional[str]] = {}

tag_data_tuple: List[Tuple[
                    Optional[Dict[str, str]],
                    List[Dict[str, Any]]]] = [
    ({"hello": "wantedId", "anotherVal": "wantedName"}, [{}])
]

for (tag_dict, data) in tag_data_tuple:

    if group_tags and tag_dict:
        if "something" in group_tags:
            pass
        else:
            insert_tags["id_value"] = tag_dict[group_tags[0].replace("\"", "")]
            if len(group_tags) > 1:
                insert_tags["name_value"] = tag_dict[group_tags[1].replace("\"", "")]

With this code the bug is reliable reproduced.
Sorry for the inconvenience.

[erictraut]

OK, thanks. I'm able to repro the problem with that code sample.

This is a core type checker issue, so I've created a tracking bug in the pyright repo.

[NielsKorschinsky]

Thanks - I am surprised, I though that pyright was integrated into pylance.

[erictraut]

Yes, pyright is integrated into pylance. Or perhaps it would be more accurate to say that pylance is built on top of pyright, at least from an architectural layering perspective. All of the core type analysis logic is in pyright, and pylance builds features on top of that capability. This particular bug is in the pyright logic.

[erictraut]

This bug will be fixed in the next release of pyright and will be picked up by pyright in some future release.

[heejaechang]

This issue has been fixed in version 2022.7.42, which we've just released. You can find the changelog here: CHANGELOG.md