Python background process not writing to MySQL db

I apologize if this question has been asked before, but I was unable to find any record of this issue. Full disclosure: I've only been using Python for a few months and MySQL for about 1 month.

I've written a short Python script on a Raspberry Pi (running Raspbian Wheezy) that sniffs wifi packets and writes signal strength info to a MySQL database. I've also created a small PHP file that grabs the info from the database and presents it in a table (pretty basic). All components of this little system work exactly as planned, however...

When I run the Python script in the background (sudo python my_script.py &) it does not appear to update the MySQL database with new readings. Yet it also throws no errors and outputs to the console without a problem (I have a line printed each time a wifi packet is intercepted and its RSSI is added to the database). I encountered the same problem when starting the script at boot up using the /etc/rc.local file. No errors, but no updates in the database either.

Is the problem on the Python side of things? A MySQL setting that I need to change? Is there something else I'm completely missing?

EDITED TO ADD CODE:

#!/usr/bin/python
# -*- coding: utf-8 -*-

import MySQLdb as mdb
import sys
from scapy.all import *

# Create connection to MySQL database called 'DATABASE' at localhost with username 'USERNAME' and password 'PASSWORD'
HOST = "localhost"
USER = "USERNAME"
PW = "PASSWORD"
DB = "DATABASE"

con = mdb.connect(HOST, USER, PW, DB)

# set interface that will be used to monitor wifi
interface = "mon0"

with con:

        cur = con.cursor()

        # This function will be called every time a packet is intercepted. Packet is passed to function as 'p'
        def sniffmgmt(p):

                # These are the 3 types of management frames that are sent exclusively by clients (allows us to weed out packets sent by APs)
                stamgmtstypes = (0, 2, 4)

                if p.haslayer(Dot11):

                        # Make sure packet is a client-only type
                        if p.subtype in stamgmtstypes:

                                # Calculate RSSI
                                sig_str = -(256-(ord(p.notdecoded[-4:-3])))

                                # Update database with most recent detection
                                cur.execute("REPLACE INTO attendance(mac_address, rssi, timestamp) VALUES('%s', %d, NOW())" % (p.addr2, sig_str))

                                # Print MAC address that was detected (debugging only)
                                print "MAC Address (%s) has been logged" % (p.addr2)

        # Tell scapy what interface to use (see above) and which function to call when a packet is intercepted. lfilter limits packets to management frames.
        sniff(iface=interface, prn=sniffmgmt, store=0, lfilter=lambda x:x.type==0)

Thanks! Kyle

P.S. For those who are wondering: this is not intended for malicious use, it is being used to investigate product tracking techniques at our warehouse.