List (or flag) mails of an IMAP account which contains a given subject text

del_imap.py

#!/usr/bin/python3

import getpass

def del_imap(server, port, login, password, search):
    import imaplib, email

    # NOTE: According to RFC 1730 the SEARCH commands searches for 'messages that
    # CONTAIN the specified string. When multiple keys are specified, the result
    # is the intersection (AND function) of all the messages that match those
    # keys.
    # _search_command = '(FROM ' + search + ')'
    # _search_command = '(SUBJECT "testmail" FROM ' + search + ')'
    _search_command = '(SUBJECT ' + search + ')'

    imapserver = imaplib.IMAP4_SSL(server, port)
    imapserver.login(login, password)
    imapserver.select()

    typ, data = imapserver.search(None, _search_command)
    if data[0]:
      for num in data[0].split():
          typ, data = imapserver.fetch(num, '(RFC822.HEADER)')
          print (data[0][1].decode())
          # Uncomment the following line if the listed files should also be
          # flagged for deletion
          #imapserver.store(num, '+FLAGS', '\\Deleted')
    imapserver.close()
    imapserver.logout()

del_imap(input("IMAP Server: "), 993, input("Username: "), getpass.getpass(), input("Search: "))

I changed this bit so it didn't melt down if the search was empty:

    typ, data = imapserver.search(None, _search_command)
    if data[0]:
      for num in data[0].split():
          typ, data = imapserver.fetch(num, '(RFC822.HEADER)')
          print (data[0][1].decode())
          # Uncomment the following line if the listed files should also be
          # flagged for deletion
          #imapserver.store(num, '+FLAGS', '\\Deleted')

Oh, thanks @redlegoman!

Although I could not test the fix, it LGFM, so I just updated the gist. Thank you!