initializing a class variable in a subclass

Question

I hope you guys can help me figure this out. I have this class:

class CsvMapping:

    __mapping = []

    @classmethod
    def initialize(cls, *args):
        if not args:
            raise AttributeError('No File/s Passed')
        
        filenames = [f for f in args]

        try:
            for file in filenames:
                with open(file, 'r') as csv_file:
                    fieldnames = csv_file.readline().split(',')
                    fieldnames = [f.strip() for f in fieldnames]

                    rows = csv.DictReader(csv_file, fieldnames=fieldnames)
                    for row in rows:
                        cls.__mapping.append(row)

        except IOError as e:
            print(strerror(e.errno))
        except AttributeError:
            print('No CsvFiles passed as arguments')
        except Exception as e:
            print(e)

    @classmethod
    def get_description_by_code(cls, code: str) -> str:
        try:
            for row in cls.__mapping:
                if row['code'] == code.upper():
                    return row['description']
        except KeyError as e:
            print('Code Not Found')

Now, I have this subclass in which I recreate the class variable (which, being private, is not supposed to be inherited) __mapping and override the get_description_by_code classmethod:

class CountryDb(CsvMapping):
    __mapping = []

    @classmethod
    def get_description_by_code(cls, code: str) -> str:
        try:
            for row in cls.__mapping:
                if row['code'] == code.upper():
                    return f"{row['description']} {row['province']}"
        except KeyError as e:
            print('Code Not Found')

what happens is I initialize the static class with something like this

    CountryDb.initialize(STATI)
    print(CountryDb.get_description_by_code('100000100'))

It does work as long as I DON'T have the method overridden. If I override the method like above, the __mapping variable of the subclass CountryDb is not used but is used to the superclass version instead. Why's that? Thank you for your help