A function gets three dataframes as an argument. Depending on it being empty or not it should copy or merge the data with an internal variable/dataframe.

    def updateMaster(self, NewLines:pd.DataFrame, Updated:pd.DataFrame, Removed:pd.DataFrame) -> bool:
                
        self.__New = self._update_dataframe(self.__New, NewLines)
        self.__Updated = self._update_dataframe(self.__Updated, Updated)
        self.__Removed = self._update_dataframe(self.__Removed, Removed)

        return True
    
    def _update_dataframe(self, dest:pd.DataFrame, source:pd.DataFrame):
        try:
            if "somecolumn" not in source.columns:
                raise ValueError("'somecolumn' as primary key is not present in data")
            #add other checks
        
        except ValueError as e:
            print(f"{e}")
            return False
        
        else:
            if dest.empty:
                dest = source.copy()
            else:
                dest = dest.merge(source, how="inner", on="somecolumn")

in no case self.__New will contain the data.

dest is self._New  # -> True

Ok so dest has the correct reference.

id(dest)
129630572847344
id(self._New)
129630572847344

Yes

dest = source.copy()

dest is self._New  # -> False

And obviously not containing the data. dest now points to another address.

Gemini suggested using copy.deepcopy() but that doesn't solve my issue.

What are my options for this problem?