Pylance does not show me the docstring for the to_csv() method

[karthiknadig]

@karthiknadig Thanks, I gave it a try but it does not yet look ready for prime to me. Without going into detail, Pylance does not show me the docstring for the to_csv() method while hovering in the following example whereas the default Python language server can do this:

pd.DataFrame([
        {'file_path': html_task.output().path}
    ]).to_csv(stream))

Feel free to create an issue for this if Pylance should be able to support this. :-)

Originally posted by @LinqLover in microsoft/vscode-python#13013 (comment)

[gramster]

I don't think this should be a "bundled typestub bug". That should only be the case if the docstring is computed and not statically declared. In this case, the docstring is available; the method is inherited from NDFrame and the docstring is at https://github.com/pandas-dev/pandas/blob/639a9c27964b09724a0ae2acdd0e6a10e49ddd88/pandas/core/generic.py#L3228. Pylance should be finding it. I am removing the label.

[jakebailey]

This issue has been fixed in version 2021.3.0, which we've just released. You can find the changelog here: https://github.com/microsoft/pylance-release/blob/main/CHANGELOG.md#202130-3-march-2021

[niderhoff]

Pylance still regularly thinks it should resolve an NDFrame while it shouldn't.
One example:

a = pd.DataFrame()
b = a.infer_objects()

b is of inferred by pyright as NDFrame. But if you click on "Go to Type Definition", you can see the method should return a FrameOrSeries:

The type stubs (right click: "Go to Declaration"), however, will show the method should return a NDFrame:

Now I have NDFrames all over my code where the stubs are broken basically. Because pylance will complaint that I cannot use basic dataframe methods because they are not implemented on the NDFrame class and the return type of the item getter __getitem__ is also not correct (it always infers the return type as None).

So I dug a little bit and found it NDFrame is implemented as an abstract class and thus has no return type.
We can see it in the pandas code:

I think the stubs are a not correctly generated with these abstract classes Pandas is using? Pyright should not infer abstract classes as return types.

Btw, trying to "cast" the NDFrames manually to a DataFrame or Series doesn't work either:

Expression of type "NDFrame" cannot be assigned to declared type "DataFrame"
  "NDFrame" is incompatible with "DataFrame"PylancereportGeneralTypeIssues

Using pandas 1.3.4 btw.