df.rename(columns=...) does not accept dict variable

[janosh]

import pandas as pd


df = pd.DataFrame(columns=["a"])

col_map = {"a": "b"}

df.rename(columns=col_map)

The above minimal example raises what appears to be a false type error on the last line due to passing columns=col_map:

Argument "columns" to "rename" of "DataFrame" has incompatible type "Dict[str, str]"; expected "Union[Mapping[Optional[Hashable], Any], Callable[[Optional[Hashable]], Optional[Hashable]], None]"mypy(error)

If instead I pass the dictionary as a literal value, the error disappears:

df.rename(columns={"a": "b"})  # all is well here

[joannasendorek]

Hi @janosh, thank you for reporting this.

It is actually really interesting issue, because we use Renamer definition directly from pandas: https://github.com/pandas-dev/pandas/blob/v1.3.2/pandas/_typing.py#L136

I was able to re-create your problem and it seems that it partly because of: python/mypy#8293
I investigating some more.