如何获取电子邮件gmail python API的主题

pip install --upgrade google-api-python-client google-auth-httplib2 google-auth-oauthlib

SCOPES = ['https://www.googleapis.com/auth/gmail.readonly']
creds = None
if os.path.exists('token.json'):
    creds = Credentials.from_authorized_user_file('token.json', SCOPES)

if not creds or not creds.valid:
    if creds and creds.expired and creds.refresh_token:
        creds.refresh(Request())
    else:
        flow = InstalledAppFlow.from_client_secrets_file('credentials.json', SCOPES)
        creds = flow.run_local_server(port=0)
    # Save the credentials for the next run
    with open('token.json', 'w') as token:
        token.write(creds.to_json())

service = build('gmail', 'v1', credentials=creds)
results = service.users().messages().list(userId='me', labelIds=['INBOX'], q='is:unread').execute()
messages = results.get('messages', [])

if not messages:
    print('No new messages.')
else:
    for message in messages:
        msg = service.users().messages().get(userId='me', id=message['id']).execute()
        subject = None
        for header in msg['payload']['headers']:
            if header['name'] == 'Subject':
                subject = header['value']
                break
        print('Subject:', subject)