Script to list emails using IMAP for the purpose of trying to **understand** how to parse emails for an ETL project

list_emails.py

from imaplib import IMAP4_SSL
import email

# Usage: python list_emails.py <hostname> <user> <password>

# https://stackoverflow.com/questions/2230037/how-to-fetch-an-email-body-using-imaplib-in-python
# Was very helpful meaning I probably copied code from there

def list_emails(hostname, user, password):
    try:
        with IMAP4_SSL(hostname, port=993) as im:
            im.login(user, password)
            # default is to select inbox
            im.select(readonly=True)
            (result, indices) = im.search(None, "ALL")

            if result == "OK":

                # Apparently its safe to assume that you will get a list of
                # length one.  I think..
                # Also fetch emails from latest to oldest
                for i in reversed(indices[0].split()):
                    (result, msg) = im.fetch(i, "(RFC822)")
                    # ALL didn't turn out what I expected.  See RFC
                    # https://tools.ietf.org/html/rfc2060.html#section-6.4.5
                    #(result, msg) = im.fetch(i, "(ALL)")
                    msg = email.message_from_string(msg[0][1].decode("utf-8"))

                    print("\n".join(["MESSAGE:"
                        , msg["Subject"]
                        , msg["From"]
                        , msg["thread-index"]
                        , msg["thread-topic"]
                        , msg["message-id"]
                        ]))

                    print("WALK:")
                    for part in msg.walk():
                        # The following line printed
                        # ['policy', '_headers', '_unixfrom', '_payload',
                        # '_charset', 'preamble', 'epilogue', 'defects',
                        # '_default_type']
                        # I was curious what else is in here..
                        # print(list(part.__dict__.keys()))

                        print("\n".join(
                            list(map(str, [part.get_content_type(),
                                part.get("content-id"),
                                # Reveals a lot of details about this part like
                                # whether this part is an attachment, filename,
                                # filesize, etc
                                part.get("content-disposition")]))
                            ))
                        print("---")

                    from email.iterators import _structure
                    print("STRUCTURE:")
                    _structure(msg)
                    print("")
            else:
                print("What happened?")
    except Exception as e:
        print(e)


if __name__ == "__main__":
    import sys
    hostname, user, password = sys.argv[1:]
    print("List emails: {0} {1}".format(hostname, user))
    list_emails(hostname, user, password)

Understanding multipart/* is crucial. The MIME wikipedia page has a subsection on it to understand at a concept/definition level of the different kinds of multiparts.