what is set_payload in python?

Question

attachment =open(filename,'rb')
part.set_payload((attachment).read())
encoders.encode_base64(part)

Answer 1

In Python, set_payload is a method of the class email.message.Message()

Answer 2

https://docs.python.org/3/library/email.compat32-message.html?highlight=set_payload#email.message.Message.set_payload

Answer 3

what is message class?