import re


def is_only_numeric(s, *args, **kwargs):
    """
    True if string `s` contains nothing but numbers (and whitespace)

    >>> is_only_numeric('Hi there')
    False

    >>> is_only_numeric('Number 9')
    False

    >>> is_only_numeric('42')
    True

    >>> is_only_numeric('  4   3 2 1')
    True

    """
    non_nums_or_spaces = re.sub(r'[\d\s]', '', s)

    return len(non_nums_or_spaces) == 0