Foundations of Python Network Programming 978-1-4302-3004-5

CHAPTER 14 ■ POP
■ Caution! As soon as a login succeeds by whatever method, some older POP servers will lock the mailbox.
Locking might mean that no alterations to the mailbox may be made, or even that no more mail may be delivered
until the lock is gone. The problem is that some POP servers do not properly detect errors, and will keep a box
locked indefinitely if your connection gets hung up without your calling quit(). At one time, the world’s most
popular POP server fell into this category!
So it is vital to always call quit() in your Python programs when finishing up a POP session. You will note that all
of the program listings shown here are careful to always quit() down in a finally block that Python is
guaranteed to execute last.
Obtaining Mailbox Information
The preceding example showed you stat(), which returns the number of messages in the mailbox and
their total size. Another useful POP command is list(), which returns more detailed information about
each message.
The most interesting part is the message number, which is required to retrieve messages later. Note
that there may be gaps in message numbers: a mailbox may, for example, contain message numbers 1, 2,
5, 6, and 9. Also, the number assigned to a particular message may be different on each connection you
make to the POP server.
Listing 14–3 shows how to use the list() command to display information about each message.
Listing 14–3. Using the POP list() Command
#!/usr/bin/env python
# POP mailbox scanning - Chapter 14 - mailbox.py
import getpass, poplib, sys
if len(sys.argv) != 3:
» print 'usage: %s hostname user' % sys.argv[0]
» exit(2)
hostname, user = sys.argv[1:]
passwd = getpass.getpass()
p = poplib.POP3_SSL(hostname)
try:
» p.user(user)
» p.pass_(passwd)
except poplib.error_proto, e:
» print "Login failed:", e
else:
» response, listings, octet_count = p.list()
» for listing in listings:
» » number, size = listing.split()
» » print "Message %s has %s bytes" % (number, size)
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