pandas groupby doesn't accept lambda functions

[Dr-Irv]

Environment data

• Language Server version: 2020.9.6
• OS and version: Windows 10
• Python version (& distribution if applicable, e.g. Anaconda): Anaconda Python 3.7.5

Expected behaviour

No error

Actual behaviour

import pandas as pd
import numpy as np

arrays = [
    ["bar", "bar", "baz", "baz", "foo", "foo", "qux", "qux"],
    ["one", "two", "one", "two", "one", "two", "one", "two"],
]


index = pd.MultiIndex.from_arrays(arrays, names=["first", "second"])

df = pd.DataFrame({"A": [1, 1, 1, 1, 2, 2, 3, 3], "B": np.arange(8)}, index=index)

g = df.groupby("A").agg(lambda x: sum(x))

print(g)

reports

No overloads for "df.groupby("A").agg(lambda x: sum(x))" match parameters
  Argument types: ((x: Unknown) -> Unknown | int)

Following seems to fix it (the changes to _typing.pyi are borrowed from the pandas source):

diff _typing.pyi.ORIG _typing.pyi
57c57,58
<
---
> FuncType = Callable[..., Any]
> F = TypeVar("F", bound=FuncType)

diff core/groupby/generic.pyi.ORIG core/groupby/generic.pyi
189c189
<     def agg(self, arg: Callable[[], Any], args, **kwargs)-> DataFrame: ...
---
>     def agg(self, arg: F, *args = ..., **kwargs = ...)-> DataFrame: ...

[jakebailey]

This issue has been fixed in version 2020.10.0, which we've just released. You can find the changelog here: https://github.com/microsoft/pylance-release/blob/master/CHANGELOG.md#2020100-7-october-2020