search and replace in a file :: newbie help

[techie2go]

hi...
i m now updating an sql file

old file contains lines
insert into mobilebill values ('Apr 01, 03', 'OUT', '91804103253', 34,
3.2);
insert into mobilebill values ('Apr 01, 03', 'OUT', '91806392475', 84,
5.2);
insert into mobilebill values ('Apr 01, 03', 'OUT', '918317048193', 76,
7.6);

i want to replace Apr 01,03 with 2003-01-03 etc...

and my script is
============
import re
lines=open('mb.sql').readlines()  #mb.sql contains the above lines
months={}
months['Jan']='01';months['Feb']='02';months['Mar']='03';months['Apr']='04'
months['May']='05';months['Jun']='06';months['Jul']='07';months['Aug']='08'
months['Sep']='09';months['Oct']='10';months['Nov']='11';months['Dec']='12'
for line in lines:
    #print line
    inp=line
    cre2=re.search('.*(\w{3}\s+\d+\,\s+\d+).*',line)
    (month,day,year)=cre2.group(1).split();
    cre3=re.compile(',')
    day=cre3.sub("",day)
    year='20'+year
    repstr=year+'-'+months[month]+'-'+day
    cre4=re.compile('.*(\w{3}\s+\d+\,\s+\d+).*')
    line=cre4.sub(repstr,line)
    print line
=================
but the output is just
2003-01-04
and not

insert into mobilebill values ('2003-01-04', 'OUT', '91804103253', 34,
3.2);

help me in this regard, what did i do wrong...
thanks and regards
gowthaman B