def is_natural_number(number, include_zero: bool = False) -> bool:
    """
    Returns True if `number` is the natural number.

    Args:
        number : an integer number to be checked.
        include_zero (bool, optional): A flag to swith to include 0
            in the natural numbers.
            Defaults to False.

    Returns:
        bool: True if `number` is the natural number.
    """
    lower_bound = 0 if include_zero else 1
    return isinstance(number, int) and number >= lower_bound