code works, but how? What does the last line do?

[Pedroski55]

I have to download 130 student photos from my email box. I am trying to get Python to do this. I can only dig up bits of code from the internet, patch them together and hope it works.

I will make a loop, but I first tried with just 1 email. This code works.

#! /usr/bin/python3
# should get image attachments from emails

import sys
import pyzmail
import email
from imapclient import IMAPClient


HOST = 'imap.qq.com'
USERNAME = '[email protected]'
PASSWORD = 'myIMAPpassword'


pathToFiles = '/home/pedro/getEmailtexts/emailTexts/'
server = IMAPClient(HOST, use_uid=True, ssl=True)
server.login(USERNAME, PASSWORD)
select_info = server.select_folder('Inbox')

rawMessage = server.fetch([59], ['BODY[]', 'FLAGS']) # I know that UID 59 has a photo, I sent it.

message = pyzmail.PyzMessage.factory(rawMessage[59][b'BODY[]'])
len(message.get_payload()) # response is 2
attachment = message.get_payload()[1]
attachment.get_content_type() # response is 'image/jpeg'
open(pathToFiles + 'rob.jpg', 'wb').write(attachment.get_payload(decode=True)) # saves the photo to my computer

Could someone please elaborate in the last line? I like to try to understand what is going on (I don't really understand).
Can this be broken into steps? What is 'wb'?

[buran]

the line is commented and is doing exactly that - save the photo (i.e. the attachment) to hard drive at pathToFiles
it is same as

with open(pathToFiles + 'rob.jpg', 'wb') as f:
    f.write(attachment.get_payload(decode=True))