Consider the following test:

def test_sum_get_add() -> None:
    df = pd.DataFrame({"x": [1,2,3,4,5], "y": [10, 20, 30, 40, 50]})
    s = df["x"]
    reveal_type(s)
    summer = df.sum(axis=1)
    reveal_type(summer)
    
    s2 = s + summer  # error is here
    s3 = s + df["y"]
    s4 = summer + summer

With the current partial stubs in main, we get the following:

Operator "+" not supported for types "Series[S1@__getitem__]" and "Series[S1@sum]"
  Operator "+" not supported for types "Series[S1@__getitem__]" and "Series[S1@sum]"
Type of "s" is "Series[S1@__getitem__]"
Type of "summer" is "Series[S1@sum]"

It's not clear to me how to resolve this. I think the right solution is to not have Series[S1] as a return type in frame.pyi and use Series instead, because a DataFrame is not a generic type dependent on S1, but maybe pyright is being too picky because it is including the method names in the types?

@gramster may need to talk to @erictraut about this.