reveal_type shows the same, but one of the objects generates an error

How come mypy warns that astype doesn't expect the variable dtypes, while it is OK to explicitly type it there?

from typing import Dict, Union
import pandas as pd

dat = pd.DataFrame(data={"A": [1], "B": [4]})

dtypes = {"A":float, "B":"int64"}
dat[[*dtypes]].astype(dtypes)  # mypy error
dat[[*dtypes]].astype({"A":float, "B":"int64"})  # no mypy error

def myf()->Dict[str, Union[str,type]]:  # this is fine
    return {"A":float, "B":"int64"}
dat[[*dtypes]].astype(myf())    # this is also fine

by calling from typing_extensions import reveal_type, it shows that both the var and the explicit definition has builtins.dict[builtins.str, builtins.object]
While the function return's type is "builtins.dict[builtins.str, Union[builtins.str, builtins.type]]"

Inizia con il reproducer Python fornito e confronta i tipi inferiti per la variabile, il dizionario inline e il valore restituito dalla funzione nella chiamata a pandas astype. Determina se le diverse diagnostiche sono intenzionali; il lavoro è concluso quando viene spiegata la causa o viene risolta la diagnostica incoerente.