A PEP8-compliant module that parses a modern Cisco serial number into an approximate date of manufacture

cisco_mfg_date.py

#!/usr/bin/env python

import re
from datetime import date, timedelta


def cisco_mfg_date(serial):
    """Parses a Cisco serial number into an approximate manufacture date.

    Modern Cisco serial numbers encode the device's year and week-of-year
    of manufacture. Returned result therefore conveys seven days of
    ambiguity.

    Args:
        serial (string): The serial number to be parsed into a date.

    Returns:
        date: A date object corresponding with the approximate date of
              manufacture

    """

    try:
        exp = r'^\s*[a-z]{3}([0-9]{2})(0[1-9]|[1-4][0-9]|5[0-2])[a-z0-9]{4}\s*$'
        m = re.match(exp, serial, re.I)
        mfg_year = 1996 + int(m.group(1))
        return date(mfg_year, 1, 1) \
            + timedelta(weeks=(int(m.group(2)))) \
            - timedelta(days=1)
    except AttributeError:
        err = '%s is not a valid Cisco serial number that ' \
              'encodes the date of manufacture.'
        raise ValueError(err % serial)