import re


def expand_serial_no(serial_strings):
    """Retrieve serial numbers from a list of strings.

    Ex. ["2..5", "8"] => [2, 3, 4, 5, 8]
    """
    case_ids = []
    for serial in serial_strings:
        result = re.match('(\d+)[.]{2}(\d+)', serial)
        if result:
            start, end = map(int, result.groups())
            case_ids.extend(range(start, end + 1))
        else:
            case_ids.append(int(serial))

    return case_ids