renames a dated file into another date format

ren_dated_file.py

#!/usr/bin/env python
#
# renames files with date JAN_18 to "<prefix> 2018-01"
# darell tan 2018.09.14
#

from __future__ import print_function
import sys
import os
import re

MONTHS = ['jan', 'feb', 'mar', 'apr', 'may', 'jun', 'jul', 'aug', 'sep', 'oct', 'nov', 'dec']

FNAME_RE = re.compile(r'.*_([A-Z]{3})_(\d+)$', re.IGNORECASE)
PREFIX = 'prefix '

def main():
    for f in sys.argv[1:]:
        if not os.path.exists(f): continue

        dirname = os.path.dirname(f)
        name, ext = os.path.splitext(f)

        m = FNAME_RE.match(name)
        if not m: continue

        month_name = m.group(1).lower()
        year = m.group(2)

        if month_name in MONTHS:
            date_str = '20%s-%02d' % (year, MONTHS.index(month_name) + 1)

        print('%s -> %s' % (f, new_fname))
        new_fname = PREFIX + date_str + ext
        os.rename(f, os.path.join(dirname, new_fname))

if __name__ == '__main__':
    main()