‘str’ object has no attribute ‘decode’. Python 3 error?

Here is my code:

import imaplib
from email.parser import HeaderParser

conn = imaplib.IMAP4_SSL('imap.gmail.com')
conn.login('example@gmail.com', 'password')
conn.select()
conn.search(None, 'ALL')
data = conn.fetch('1', '(BODY[HEADER])')
header_data = data[1][0][1].decode('utf-8')

at this point I get the error message

AttributeError: 'str' object has no attribute 'decode'

Python 3 doesn’t have decode anymore, am I right? how can I fix this?

Also, in:

data = conn.fetch('1', '(BODY[HEADER])')

I am selecting only the 1st email. How do I select all?