def METHOD_NAME(*, username:str, email:str) -> (bool, str):
    """
    Checks if a specified user is already registred.
    Returns a tuple containing a boolean value that indicates if the user exists
    and in case he does whats the duplicated attribute
    """
    user_model = get_user_model()
    if user_model.objects.filter(username__iexact=username).exists():
        return (True, _("Username is already in use."))
    if user_model.objects.filter(email__iexact=email).exists():
        return (True, _("Email is already in use."))
    return (False, None)