Pylance intellisense does not highlight object methods in case of its creation with different arg types

[wvolkov]

Environment data

• Language Server version: 2021.9.3 (pyright d2771b18)
• OS and version: Ubuntu 20.04
• Python version (& distribution if applicable, e.g. Anaconda): 3.7

Code Snippet / Additional information

Assume class DecisionEngine, which creates an instance of DBClient, passing an integer instead of string as specified below:

class DBClient:

    def __init__(self, param: str):
        self.param = param

    async def setup(self):
        pass

class DecisionEngine:

    def __init__(self):
        self.db: DBClient = None

    async def setup(self):
        self.db = DBClient(1)
        await self.db.setup()

Expected behaviour

at setup method of DecisionEngine class it is possible to drill down into setup method of db object:

Actual behaviour

it interprets db object as Any type despite the fact that it is correctly recognize the type of db object at upper line of code

[jakebailey]

This seems like a bug in some async handling, at least in the hover; repeat the same thing and I get:

Making setup return something lets me see:

[erictraut]

First, there's a type error in the sample above. The expression DBClient(1) isn't valid because the constructor for DBClient accepts a str, not an int. If you enable type checking, this error will be flagged.

Second, I'm not able to repro the behavior you're seeing @jakebailey. I can't see all of your code, so perhaps there are differences? Where is the value of 1234 coming from? Here's what I see:

from typing import Optional

class DBClient:
    def __init__(self, param: str):
        self.param = param

    async def setup(self):
        pass

class DecisionEngine:
    def __init__(self):
        self.db: Optional[DBClient] = None

    async def setup(self):
        self.db = DBClient("1")
        reveal_type(await self.db.setup())

[jakebailey]

The code I have is this:

class DBClient:
    def __init__(self, param: str):
        self.param = param

    async def setup(self):
        return 1234

class DecisionEngine:
    def __init__(self):
        self.db: DBClient = None

    async def setup(self):
        self.db = DBClient(1)

        self.db.setup()
        await self.db.setup()

        reveal_type(self.db.setup())
        reveal_type(await self.db.setup())

Revealing the type produces the right result, but try hovering on db inside of the await and compare it to outside of the await. Hovering on it within reveal_type also says it's Any.

Similarly on setup in each of the uses inside the engine class.

[jakebailey]

I did a bit of debugging, and our hover code sees that it's a name node (it being db), then asks for declarations from the type evaluator, but when it does getType, it returns undefined. (That's as far as I went to debug before seeing it was going to be an evaluator thing.)

[wvolkov]

First, there's a type error in the sample above. The expression DBClient(1) isn't valid because the constructor for DBClient accepts a str, not an int. If you enable type checking, this error will be flagged.

Second, I'm not able to repro the behavior you're seeing @jakebailey. I can't see all of your code, so perhaps there are differences? Where is the value of 1234 coming from? Here's what I see:

from typing import Optional

class DBClient:
    def __init__(self, param: str):
        self.param = param

    async def setup(self):
        pass

class DecisionEngine:
    def __init__(self):
        self.db: Optional[DBClient] = None

    async def setup(self):
        self.db = DBClient("1")
        reveal_type(await self.db.setup())

I didn't see any type error at VS Code, why?

[jakebailey]

@wvolkov Type checking isn't enabled by default in Pylance; you need to set python.analysis.typeCheckingMode or set it in a pyrightconfig.json.

[jakebailey]

Ah, so fixing the type error fixes this. That's interesting.

I'm not really sure why that would be the case, if reveal_type gets the right answer, and it works here:

[erictraut]

Yes, good catch. There is a bug here that causes the hover type for self.db to appears as Unknown even though it is eventually resolved to DBClient. The problem is that the logic that evaluates the type for the await statement was not honoring the "incomplete" flag and was marking the type evaluation for itself as completely resolved. A fix for this bug will be included in the next release.

[jakebailey]

This issue has been fixed in version 2021.9.4, which we've just released. You can find the changelog here: https://github.com/microsoft/pylance-release/blob/main/CHANGELOG.md#202194-29-september-2021