New version from Piers Lauder, who writes:

Added a debug function to replace 'print' statements.
Ensured that response attached to 'NO' replies is passed back.
added readonly exception.
Rearranged method order into types.
Ensure select returns a meaningful error on 'NO'.
'NO' returns from authenticate and login raise error with last message,
not list.

Lib/imaplib.py

@@ -15,9 +15,9 @@ Public functions:	Internaldate2tuple
 			Time2Internaldate
 """
 
-__version__ = "2.11"
+__version__ = "2.15"
 
-import binascii, re, socket, string, time, random
+import binascii, re, socket, string, time, random, sys
 
 #	Globals
 
@@ -97,7 +97,9 @@ class IMAP4:
 
 	Errors raise the exception class <instance>.error("<reason>").
 	IMAP4 server errors raise <instance>.abort("<reason>"),
-	which is a sub-class of 'error'.
+	which is a sub-class of 'error'. Mailbox status changes
+	from READ-WRITE to READ-ONLY raise the exception class
+	<instance>.readonly("<reason>"), which is a sub-class of 'abort'.
 
 	Note: to use this module, you must read the RFCs pertaining
 	to the IMAP4 protocol, as the semantics of the arguments to
@@ -107,6 +109,7 @@ class IMAP4:
 
 	class error(Exception): pass	# Logical errors - debug required
 	class abort(error): pass	# Service errors - close and retry
+	class readonly(abort): pass	# Mailbox status changed to READ-ONLY
 
 
 	def __init__(self, host = '', port = IMAP4_PORT):
@@ -136,7 +139,7 @@ class IMAP4:
 		# request and store CAPABILITY response.
 
 		if __debug__ and self.debug >= 1:
-			print '\tnew IMAP4 connection, tag=%s' % self.tagpre
+			_mesg('new IMAP4 connection, tag=%s' % self.tagpre)
 
 		self.welcome = self._get_response()
 		if self.untagged_responses.has_key('PREAUTH'):
@@ -154,7 +157,7 @@ class IMAP4:
 		self.capabilities = tuple(string.split(self.untagged_responses[cap][-1]))
 
 		if __debug__ and self.debug >= 3:
-			print '\tCAPABILITIES: %s' % `self.capabilities`
+			_mesg('CAPABILITIES: %s' % `self.capabilities`)
 
 		for version in AllowedVersions:
 			if not version in self.capabilities:
@@ -165,6 +168,17 @@ class IMAP4:
 		raise self.error('server not IMAP4 compliant')
 
 
+	def __getattr__(self, attr):
+		#	Allow UPPERCASE variants of IMAP4 command methods.
+		if Commands.has_key(attr):
+			return eval("self.%s" % string.lower(attr))
+		raise AttributeError("Unknown IMAP4 command: '%s'" % attr)
+
+
+
+	#	Public methods
+
+
 	def open(self, host, port):
 		"""Setup 'self.sock' and 'self.file'."""
 		self.sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
@@ -172,14 +186,43 @@ class IMAP4:
 		self.file = self.sock.makefile('r')
 
 
-	def __getattr__(self, attr):
-		"""Allow UPPERCASE variants of all following IMAP4 commands."""
-		if Commands.has_key(attr):
-			return eval("self.%s" % string.lower(attr))
-		raise AttributeError("Unknown IMAP4 command: '%s'" % attr)
+	def recent(self):
+		"""Return most recent 'RECENT' responses if any exist,
+		else prompt server for an update using the 'NOOP' command.
 
+		(typ, [data]) = <instance>.recent()
+
+		'data' is None if no new messages,
+		else list of RECENT responses, most recent last.
+		"""
+		name = 'RECENT'
+		typ, dat = self._untagged_response('OK', [None], name)
+		if dat[-1]:
+			return typ, dat
+		typ, dat = self.noop()	# Prod server for response
+		return self._untagged_response(typ, dat, name)
+
+
+	def response(self, code):
+		"""Return data for response 'code' if received, or None.
+
+		Old value for response 'code' is cleared.
+
+		(code, [data]) = <instance>.response(code)
+		"""
+		return self._untagged_response(code, [None], string.upper(code))
+
+
+	def socket(self):
+		"""Return socket instance used to connect to IMAP4 server.
+
+		socket = <instance>.socket()
+		"""
+		return self.sock
 
-	#	Public methods
+
+
+	#	IMAP4 commands
 
 
 	def append(self, mailbox, flags, date_time, message):
@@ -224,7 +267,7 @@ class IMAP4:
 		self.literal = _Authenticator(authobject).process
 		typ, dat = self._simple_command('AUTHENTICATE', mech)
 		if typ != 'OK':
-			raise self.error(dat)
+			raise self.error(dat[-1])
 		self.state = 'AUTH'
 		return typ, dat
 
@@ -246,8 +289,7 @@ class IMAP4:
 		(typ, [data]) = <instance>.close()
 		"""
 		try:
-			try: typ, dat = self._simple_command('CLOSE')
-			except EOFError: typ, dat = None, [None]
+			typ, dat = self._simple_command('CLOSE')
 		finally:
 			self.state = 'AUTH'
 		return typ, dat
@@ -288,7 +330,7 @@ class IMAP4:
 		"""
 		name = 'EXPUNGE'
 		typ, dat = self._simple_command(name)
-		return self._untagged_response(typ, name)
+		return self._untagged_response(typ, dat, name)
 
 
 	def fetch(self, message_set, message_parts):
@@ -300,7 +342,7 @@ class IMAP4:
 		"""
 		name = 'FETCH'
 		typ, dat = self._simple_command(name, message_set, message_parts)
-		return self._untagged_response(typ, name)
+		return self._untagged_response(typ, dat, name)
 
 
 	def list(self, directory='""', pattern='*'):
@@ -312,7 +354,7 @@ class IMAP4:
 		"""
 		name = 'LIST'
 		typ, dat = self._simple_command(name, directory, pattern)
-		return self._untagged_response(typ, name)
+		return self._untagged_response(typ, dat, name)
 
 
 	def login(self, user, password):
@@ -322,7 +364,7 @@ class IMAP4:
 		"""
 		typ, dat = self._simple_command('LOGIN', user, password)
 		if typ != 'OK':
-			raise self.error(dat)
+			raise self.error(dat[-1])
 		self.state = 'AUTH'
 		return typ, dat
 
@@ -336,7 +378,7 @@ class IMAP4:
 		"""
 		self.state = 'LOGOUT'
 		try: typ, dat = self._simple_command('LOGOUT')
-		except EOFError: typ, dat = None, [None]
+		except: typ, dat = 'NO', ['%s: %s' % sys.exc_info()[:2]]
 		self.file.close()
 		self.sock.close()
 		if self.untagged_responses.has_key('BYE'):
@@ -353,7 +395,7 @@ class IMAP4:
 		"""
 		name = 'LSUB'
 		typ, dat = self._simple_command(name, directory, pattern)
-		return self._untagged_response(typ, name)
+		return self._untagged_response(typ, dat, name)
 
 
 	def noop(self):
@@ -362,7 +404,7 @@ class IMAP4:
 		(typ, data) = <instance>.noop()
 		"""
 		if __debug__ and self.debug >= 3:
-			print '\tuntagged responses: %s' % `self.untagged_responses`
+			_dump_ur(self.untagged_responses)
 		return self._simple_command('NOOP')
 
 
@@ -375,26 +417,7 @@ class IMAP4:
 		"""
 		name = 'PARTIAL'
 		typ, dat = self._simple_command(name, message_num, message_part, start, length)
-		return self._untagged_response(typ, 'FETCH')
-
-
-	def recent(self):
-		"""Return most recent 'RECENT' responses if any exist,
-		else prompt server for an update using the 'NOOP' command,
-		and flush all untagged responses.
-
-		(typ, [data]) = <instance>.recent()
-
-		'data' is None if no new messages,
-		else list of RECENT responses, most recent last.
-		"""
-		name = 'RECENT'
-		typ, dat = self._untagged_response('OK', name)
-		if dat[-1]:
-			return typ, dat
-		self.untagged_responses = {}
-		typ, dat = self._simple_command('NOOP')
-		return self._untagged_response(typ, name)
+		return self._untagged_response(typ, dat, 'FETCH')
 
 
 	def rename(self, oldmailbox, newmailbox):
@@ -405,16 +428,6 @@ class IMAP4:
 		return self._simple_command('RENAME', oldmailbox, newmailbox)
 
 
-	def response(self, code):
-		"""Return data for response 'code' if received, or None.
-
-		Old value for response 'code' is cleared.
-
-		(code, [data]) = <instance>.response(code)
-		"""
-		return self._untagged_response(code, string.upper(code))
-
-
 	def search(self, charset, criteria):
 		"""Search mailbox for matching messages.
 
@@ -426,7 +439,7 @@ class IMAP4:
 		if charset:
 			charset = 'CHARSET ' + charset
 		typ, dat = self._simple_command(name, charset, criteria)
-		return self._untagged_response(typ, name)
+		return self._untagged_response(typ, dat, name)
 
 
 	def select(self, mailbox='INBOX', readonly=None):
@@ -445,23 +458,17 @@ class IMAP4:
 		else:
 			name = 'SELECT'
 		typ, dat = self._simple_command(name, mailbox)
-		if typ == 'OK':
-			self.state = 'SELECTED'
-		elif typ == 'NO':
-			self.state = 'AUTH'
-		if not readonly and not self.untagged_responses.has_key('READ-WRITE'):
-			raise self.error('%s is not writable' % mailbox)
+		if typ != 'OK':
+			self.state = 'AUTH'	# Might have been 'SELECTED'
+			return typ, dat
+		self.state = 'SELECTED'
+		if not self.untagged_responses.has_key('READ-WRITE') \
+			and not readonly:
+			if __debug__ and self.debug >= 1: _dump_ur(self.untagged_responses)
+			raise self.readonly('%s is not writable' % mailbox)
 		return typ, self.untagged_responses.get('EXISTS', [None])
 
 
-	def socket(self):
-		"""Return socket instance used to connect to IMAP4 server.
-
-		socket = <instance>.socket()
-		"""
-		return self.sock
-
-
 	def status(self, mailbox, names):
 		"""Request named status conditions for mailbox.
 
@@ -471,7 +478,7 @@ class IMAP4:
 		if self.PROTOCOL_VERSION == 'IMAP4':
 			raise self.error('%s unimplemented in IMAP4 (obtain IMAP4rev1 server, or re-code)' % name)
 		typ, dat = self._simple_command(name, mailbox, names)
-		return self._untagged_response(typ, name)
+		return self._untagged_response(typ, dat, name)
 
 
 	def store(self, message_set, command, flag_list):
@@ -480,7 +487,7 @@ class IMAP4:
 		(typ, [data]) = <instance>.store(message_set, command, flag_list)
 		"""
 		typ, dat = self._simple_command('STORE', message_set, command, flag_list)
-		return self._untagged_response(typ, 'FETCH')
+		return self._untagged_response(typ, dat, 'FETCH')
 
 
 	def subscribe(self, mailbox):
@@ -511,9 +518,7 @@ class IMAP4:
 			name = 'SEARCH'
 		else:
 			name = 'FETCH'
-		typ, dat2 = self._untagged_response(typ, name)
-		if dat2[-1]: dat = dat2
-		return typ, dat
+		return self._untagged_response(typ, dat, name)
 
 
 	def unsubscribe(self, mailbox):
@@ -542,12 +547,13 @@ class IMAP4:
 	def _append_untagged(self, typ, dat):
 
 		ur = self.untagged_responses
+		if __debug__ and self.debug >= 5:
+			_mesg('untagged_responses[%s] %s += %s' %
+				(typ, len(ur.get(typ,'')), dat))
 		if ur.has_key(typ):
 			ur[typ].append(dat)
 		else:
 			ur[typ] = [dat]
-		if __debug__ and self.debug >= 5:
-			print '\tuntagged_responses[%s] %s += %s' % (typ, len(`ur[typ]`), _trunc(20, `dat`))
 
 
 	def _command(self, name, *args):
@@ -557,8 +563,14 @@ class IMAP4:
 			raise self.error(
 			'command %s illegal in state %s' % (name, self.state))
 
-		if self.untagged_responses.has_key('OK'):
-			del self.untagged_responses['OK']
+		for typ in ('OK', 'NO', 'BAD'):
+			if self.untagged_responses.has_key(typ):
+				del self.untagged_responses[typ]
+
+		if self.untagged_responses.has_key('READ-WRITE') \
+		and self.untagged_responses.has_key('READ-ONLY'):
+			del self.untagged_responses['READ-WRITE']
+			raise self.readonly('mailbox status changed to READ-ONLY')
 
 		tag = self._new_tag()
 		data = '%s %s' % (tag, name)
@@ -588,7 +600,7 @@ class IMAP4:
 			raise self.abort('socket error: %s' % val)
 
 		if __debug__ and self.debug >= 4:
-			print '\t> %s' % data
+			_mesg('> %s' % data)
 
 		if literal is None:
 			return tag
@@ -606,7 +618,7 @@ class IMAP4:
 				literal = literator(self.continuation_response)
 
 			if __debug__ and self.debug >= 4:
-				print '\twrite literal size %s' % len(literal)
+				_mesg('write literal size %s' % len(literal))
 
 			try:
 				self.sock.send(literal)
@@ -684,7 +696,7 @@ class IMAP4:
 
 				size = string.atoi(self.mo.group('size'))
 				if __debug__ and self.debug >= 4:
-					print '\tread literal size %s' % size
+					_mesg('read literal size %s' % size)
 				data = self.file.read(size)
 
 				# Store response with literal as tuple
@@ -702,6 +714,9 @@ class IMAP4:
 		if typ in ('OK', 'NO', 'BAD') and self._match(Response_code, dat):
 			self._append_untagged(self.mo.group('type'), self.mo.group('data'))
 
+		if __debug__ and self.debug >= 1 and typ in ('NO', 'BAD'):
+			_mesg('%s response: %s' % (typ, dat))
+
 		return resp
 
 
@@ -719,13 +734,13 @@ class IMAP4:
 
 		line = self.file.readline()
 		if not line:
-			raise EOFError
+			raise self.abort('socket error: EOF')
 
 		# Protocol mandates all lines terminated by CRLF
 
 		line = line[:-2]
 		if __debug__ and self.debug >= 4:
-			print '\t< %s' % line
+			_mesg('< %s' % line)
 		return line
 
 
@@ -736,7 +751,7 @@ class IMAP4:
 
 		self.mo = cre.match(s)
 		if __debug__ and self.mo is not None and self.debug >= 5:
-			print "\tmatched r'%s' => %s" % (cre.pattern, `self.mo.groups()`)
+			_mesg("\tmatched r'%s' => %s" % (cre.pattern, `self.mo.groups()`))
 		return self.mo is not None
 
 
@@ -753,13 +768,15 @@ class IMAP4:
 		return self._command_complete(name, apply(self._command, (name,) + args))
 
 
-	def _untagged_response(self, typ, name):
+	def _untagged_response(self, typ, dat, name):
 
+		if typ == 'NO':
+			return typ, dat
 		if not self.untagged_responses.has_key(name):
 			return typ, [None]
 		data = self.untagged_responses[name]
 		if __debug__ and self.debug >= 5:
-			print '\tuntagged_responses[%s] => %s' % (name, _trunc(20, `data`))
+			_mesg('untagged_responses[%s] => %s' % (name, data))
 		del self.untagged_responses[name]
 		return typ, data
 
@@ -905,9 +922,19 @@ def Time2Internaldate(date_time):
 
 if __debug__:
 
-	def _trunc(m, s):
-		if len(s) <= m: return s
-		return '%.*s..' % (m, s)
+	def _mesg(s):
+#		if len(s) > 70: s = '%.70s..' % s
+		sys.stderr.write('\t'+s+'\n')
+		sys.stderr.flush()
+
+	def _dump_ur(dict):
+		# Dump untagged responses (in `dict').
+		l = dict.items()
+		if not l: return
+		t = '\n\t\t'
+		j = string.join
+		l = map(lambda x,j=j:'%s: "%s"' % (x[0], x[1][0] and j(x[1], '" "') or ''), l)
+		_mesg('untagged responses dump:%s%s' % (t, j(l, t)))
 
 
 
@@ -947,12 +974,12 @@ if __debug__ and __name__ == '__main__':
 
 	def run(cmd, args):
 		typ, dat = apply(eval('M.%s' % cmd), args)
-		print ' %s %s\n  => %s %s' % (cmd, args, typ, dat)
+		_mesg(' %s %s\n  => %s %s' % (cmd, args, typ, dat))
 		return dat
 
 	Debug = 5
 	M = IMAP4(host)
-	print 'PROTOCOL_VERSION = %s' % M.PROTOCOL_VERSION
+	_mesg('PROTOCOL_VERSION = %s' % M.PROTOCOL_VERSION)
 
 	for cmd,args in test_seq1:
 		run(cmd, args)