import re


def __is_rut_format(rut: str) -> bool:
    """
    Validates if given string have Chilean RUT Number format

    Args:
        rut (str):  A Chilean RUT Number. For example 5.126.663-3  | 5126663-3 | 51266633

    Returns:
        bool: True when given string is a Chilean RUT number format
        ** Only validates the format not if the RUT is valid or not
    """
    format_rut_regex = r"^0*(\d{1,3}(\.?\d{3})*)-?([\dkK])$"
    return re.match(format_rut_regex, str(rut)) is not None