import re


def number_format(number_string, fill=2):
    """
    add padding zeros to make alinged numbers
    ex. 

    >>> number_format('2')
    '02'

    >>> number_format('1-2')
    '01-02'
    """
    output = []
    digits_spliter = r'(?P<digit>\d+)|(?P<nondigit>.)'
    for token in [m.groups() for m in re.finditer(digits_spliter, number_string)]:
        if token[0] is None:
            output.append(token[1])
        else:
            output.append(token[0].zfill(2))
    return ''.join(output)