def make_numbered_prefix(file_number,number_digits=5):
    """
    returns a number string designed to be used in the prefix of
    systematic outputs.

    example use case
        "00001example_output_file.txt"
        "00002example_output_file.txt"

    Args:
        file_number (int): the number you want to prefix
        number_digits (int): minimum number of digits in the output
            string. Default is 5
    Returns:
        str: string of numbers with standard at least
            'number_digits' of digits
    """
    file_number = int( file_number )
    if file_number < 0:
        file_number_is_negative = True
    else:
        file_number_is_negative = False

    file_number_string = str( abs(file_number) )
    len_num_string = len(file_number_string)

    if len_num_string < number_digits:
        prefix = '0' * int(number_digits - len_num_string)
    else:
        prefix = ''

    if file_number_is_negative:
        prefix = '-' + prefix

    numbered_string = prefix + file_number_string
    return numbered_string