Str Object Has No Attribute Decode

How to resolve the python error str object has no attribute decode?

I am getting an error called str object has no attribute decode please help me here is my code:

import imaplib 

from email.parser import HeaderParser 

conn = imaplib.IMAP4_SSL('imap.gmail.com') 

conn.login('mindmajix@gmail.com', 'password') 

conn.select() conn.search(None, 'ALL') 

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

header_data = data[1][0][1].decode('utf-8')