def parse_parameter_code(match):
    """Process a regular expression match for a parameter code and a description.
    The parameter code and description string line is made up of 4 parts:

    1. a data descriptor value

    2. a parameter code value

    3. a parameter statistic value (may or may not exist)

    4. a parameter description

    :param match: a regular expression match object
    :type match: _sre.SRE_Match
    :return: parameter code, statistic (if it exists), and description
    :rtype: tuple

    >>> import re
    >>> parameter_code_re = "(#)\D+([0-9]{2})\D+([0-9]{5})(\D+[0-9]{5})?(.+)"
    >>> line = "#\t06\t00060\t00003\tDischarge, cubic feet per second (Mean)"
    >>> match = re.search(rdb.parameter_code_re, line)
    >>> parameter_code = rdb.parse_parameter_code(match)
    >>> parameter_code
    ('06_00060_00003', 'Discharge, cubic feet per second (Mean)')
    """
    # get the data descriptor and the parameter code
    dd = match.group(2)
    param = match.group(3)

    # concatenate dd and param using "_" as in the column names
    code = "_".join((dd, param))

    # get parameter description
    description = match.group(5).strip()

    # if statistic exists, then add that to the string
    if match.group(4):
        statistic =  match.group(4).strip()
        code = "_".join((code, statistic))

    return (code, description)