Fix _proc_folder_list quadratic runtime (mjs#374)

Author: carsonip

imapclient/imapclient.py

@@ -25,7 +25,7 @@
 from .datetime_util import datetime_to_INTERNALDATE, format_criteria_date
 from .imap_utf7 import encode as encode_utf7, decode as decode_utf7
 from .response_parser import parse_response, parse_message_list, parse_fetch_response
-from .util import to_bytes, to_unicode, assert_imap_protocol
+from .util import to_bytes, to_unicode, assert_imap_protocol, chunk
 xrange = moves.xrange
 
 if PY3:
@@ -609,11 +609,7 @@ def _proc_folder_list(self, folder_data):
 
         ret = []
         parsed = parse_response(folder_data)
-        while parsed:
-            # TODO: could be more efficient
-            flags, delim, name = parsed[:3]
-            parsed = parsed[3:]
-
+        for flags, delim, name in chunk(parsed, size=3):
             if isinstance(name, (int, long)):
                 # Some IMAP implementations return integer folder names
                 # with quotes. These get parsed to ints so convert them

imapclient/util.py

@@ -4,6 +4,7 @@
 
 from __future__ import unicode_literals
 
+import six
 import logging
 from six import binary_type, text_type
 
@@ -37,3 +38,8 @@ def assert_imap_protocol(condition, message=None):
         if message:
             msg += "{}: {}".format(msg, message)
         raise exceptions.ProtocolError(msg)
+
+
+def chunk(lst, size):
+    for i in six.moves.range(0, len(lst), size):
+        yield lst[i:i + size]