Why is pyright issuing a type incompatibility error here?

Question

from pandas import DataFrame, Series

# This function prunes the dataframe rows to those meeting specified criteria
def prune_to_wanted_rows(st_df: DataFrame, recency_date: str) -> DataFrame:
    st_df = st_df[ # pyright error message (see below) here
        (st_df["assetType"] == "ore")
        & (st_df["priceCurrency"] == "USD")
        & (st_df["endDate"] >= recency_date)
        # other boolean expressions omitted for brevity
    ]
    return st_df

The error message, all on the one line, with hyphens here replacing some spaces, is:

Expression of type "Series | Unknown | DataFrame" is incompatible with declared type "DataFrame"------Type "Series | Unknown | DataFrame" is incompatible with type "DataFrame"------Type "Series" is incompatible with "DataFrame"

I think this is only a problem because the error message is ugly. I can suppress it with # pyright: ignore and the code works as intended. I don't (yet) see a type incompatibility, but is there a sense in which pyright is "right"?

Answer 1

Changing st_df = st_df[ to st_def = st_df.loc[ prevents the error message.