what_day.py

from datetime import datetime as dt

def main() -> None:
    while True:
        weekdays: list[str] = ['월', '화', '수', '목', '금', '토', '일']
        date_string: str = input('날짜를 입력해 주세요(YYYY-MM-DD): ')
        date = dt(int((date_list:=date_string.split('-'))[0]), int(date_list[1]), int(date_list[2]))
        print(f'{date_string}은 {weekdays[date.weekday()]}요일입니다.')

if __name__ == '__main__':
    main()