Overwrite JPG file if it already exists Python script

I cannot figure out why the following script will not overwrite a file with the same name. I've used chmod 777 and the directory is writeable. The script executes perfectly when a new file is retrieved, however it doesn't not replace existing files and desired.

this script crawls through Gmail, looks for a subject line and retrieves attachments to the correct directory.

#!/usr/bin python3
# read emails and detach attachment in attachments directory
 
import email
import getpass, imaplib
import os
import sys
import time

detach_dir =  '/var/www/html/attachments'
if not os.path.exists(detach_dir):
    os.makedirs(detach_dir)

userName = 'username'
passwd = 'password'
 
try:
    imapSession = imaplib.IMAP4_SSL('imap.gmail.com',993)
    typ, accountDetails = imapSession.login(userName, passwd)
    if typ != 'OK':
        print ('Not able to sign in!')
        raise Exception
 
    imapSession.select('Inbox')
    typ, data = imapSession.search(None, 'SUBJECT', '"IMAGES"')
    if typ != 'OK':
        print ('Error searching Inbox.')
        raise Exception

    for msgId in data[0].split():
        typ, messageParts = imapSession.fetch(msgId, '(RFC822)')
 
        if typ != 'OK':
            print ('Error fetching mail.')
            raise Exception
 
        emailBody = messageParts[0][1] 
        mail = email.message_from_bytes(emailBody) 
 
        for part in mail.walk():
 
            if part.get_content_maintype() == 'multipart':
 
                continue
            if part.get('Content-Disposition') is None:
 
                continue
 
            fileName = part.get_filename()
 
            if bool(fileName): 
                filePath = os.path.join(detach_dir, fileName)
                if not os.path.isfile(filePath) : 
                    print (fileName)
                    print (filePath)
                    fp = open(filePath, 'wb')
                    fp.write(part.get_payload(decode=True))
                    fp.close()
 
    #MOVING EMAILS TO PROCESSED PART BEGINS HERE
    imapSession.select(mailbox='inbox', readonly=False)
    resp, items = imapSession.search(None, 'All')
    email_ids = items[0].split()
    for email in email_ids:
        latest_email_id = email
 
        #move to processed
        result = imapSession.store(latest_email_id, '+X-GM-LABELS', 'Processed')
 
        if result[0] == 'OK':
            #delete from inbox
            imapSession.store(latest_email_id, '+FLAGS', '\\Deleted')
 
    #END OF MOVING EMAILS TO PROCESSED
 
    imapSession.close()
    imapSession.logout()
 
except :
    print ('No attachments were downloaded')

Any thoughts on what I need to change to have the file be overwritten if a file of the same name already exists?