Issue with concat and passing a Union due to presence of checking for Iterable[None]

[Dr-Irv]

You are right, the example doesn't work, my bad. This example does work though, and the same question still applies.

data: pd.DataFrame | pd.Series = pd.Series()

pd.concat([pd.DataFrame(), data])

returns

error: List item 0 has incompatible type "DataFrame"; expected "None"  [list-item]
error: List item 1 has incompatible type "DataFrame | Series[Any]"; expected "None"  [list-item]

Originally posted by @tvdboom in #878 (comment)

[Dr-Irv]

The above code triggers issues with pyright and mypy. Interestingly, if we remove the first overload for pd.concat that looks for Iterable[None], then the above code type checks correctly.

Going to see what @twoertwein thinks - he put that in there.

[twoertwein]

I assumed you can only concat DataFrame and Series along axis=1. seems you can also do it for axis=0:

>>> pd.concat([pd.DataFrame([[0, 1], [2, 3]]), pd.Series([4,5])])
   0    1
0  0  1.0
1  2  3.0
0  4  NaN
1  5  NaN