diff --git a/pykolab/itip/__init__.py b/pykolab/itip/__init__.py
--- a/pykolab/itip/__init__.py
+++ b/pykolab/itip/__init__.py
@@ -1,26 +1,33 @@
-import icalendar
-import pykolab
+import re
 import traceback
+
+import icalendar
 import kolabformat
-import re
 
+import pykolab
+from pykolab.translate import _
 from pykolab.xml import to_dt
 from pykolab.xml import event_from_ical
 from pykolab.xml import todo_from_ical
 from pykolab.xml import participant_status_label
-from pykolab.translate import _
+
 from tzlocal import windows_tz
 
+# pylint: disable=invalid-name
 log = pykolab.getLogger('pykolab.wallace')
 
 
 def events_from_message(message, methods=None):
     return objects_from_message(message, ["VEVENT"], methods)
 
+
 def todos_from_message(message, methods=None):
     return objects_from_message(message, ["VTODO"], methods)
 
-def objects_from_message(message, objnames, methods=None):
+
+# pylint: disable=too-many-branches
+# pylint: disable=too-many-statements
+def objects_from_message(message, objnames, methods=None):  # noqa: C901
     """
         Obtain the iTip payload from email.message <message>
     """
@@ -30,7 +37,7 @@
 
     # iTip methods we are actually interested in. Other methods will be ignored.
     if methods is None:
-        methods = [ "REQUEST", "CANCEL" ]
+        methods = ["REQUEST", "CANCEL"]
 
     # Are all iTip messages multipart? No! RFC 6047, section 2.4 states "A
     # MIME body part containing content information that conforms to this
@@ -38,19 +45,23 @@
     # therefore also be multipart.
 
     # Check each part
+    # pylint: disable=too-many-nested-blocks
     for part in message.walk():
 
         # The iTip part MUST be Content-Type: text/calendar (RFC 6047, section 2.4)
         # But in real word, other mime-types are used as well
-        if part.get_content_type() in [ "text/calendar", "text/x-vcalendar", "application/ics" ]:
-            if not str(part.get_param('method')).upper() in methods:
-                log.info(_("Method %r not really interesting for us.") % (part.get_param('method')))
+        if part.get_content_type() in ["text/calendar", "text/x-vcalendar", "application/ics"]:
+            if str(part.get_param('method')).upper() not in methods:
+                log.info("Method %r not really interesting for us." % (part.get_param('method')))
                 continue
 
             # Get the itip_payload
             itip_payload = part.get_payload(decode=True)
 
-            log.debug(_("Raw iTip payload (%r): %r") % (part.get_param('charset'), itip_payload), level=8)
+            log.debug(
+                "Raw iTip payload (%r): %r" % (part.get_param('charset'), itip_payload),
+                level=8
+            )
 
             # Convert unsupported timezones, etc.
             itip_payload = _convert_itip_payload(itip_payload)
@@ -90,33 +101,37 @@
                     itip['type'] = 'task' if c.name == 'VTODO' else 'event'
                     itip['uid'] = str(c['uid'])
                     itip['method'] = str(cal['method']).upper()
-                    itip['sequence'] = int(c['sequence']) if c.has_key('sequence') else 0
-                    itip['recurrence-id'] = c['recurrence-id'].dt if c.has_key('recurrence-id') and hasattr(c['recurrence-id'], 'dt') else None
+                    itip['sequence'] = int(c['sequence']) if 'sequence' in c else 0
 
-                    if c.has_key('dtstart'):
+                    itip['recurrence-id'] = None
+                    if 'recurrence-id' in c:
+                        if hasattr(c['recurrence-id'], 'dt'):
+                            itip['recurrence-id'] = c['recurrence-id'].dt
+
+                    if 'dtstart' in c:
                         itip['start'] = c['dtstart'].dt
                     elif itip['type'] == 'event':
                         log.error(_("iTip event without a start"))
                         continue
 
-                    if c.has_key('dtend'):
+                    if 'dtend' in c:
                         itip['end'] = c['dtend'].dt
 
-                    if c.has_key('duration'):
+                    if 'duration' in c:
                         itip['duration'] = c['duration'].dt
                         itip['end'] = itip['start'] + c['duration'].dt
 
                     # Outlook can send itip replies with no organizer property
-                    if c.has_key('organizer'):
+                    if 'organizer' in c:
                         itip['organizer'] = c['organizer']
 
-                    if c.has_key('attendee'):
+                    if 'attendee' in c:
                         itip['attendees'] = c['attendee']
 
-                    if itip.has_key('attendees') and not isinstance(itip['attendees'], list):
+                    if 'attendees' in itip and not isinstance(itip['attendees'], list):
                         itip['attendees'] = [c['attendee']]
 
-                    if c.has_key('resources'):
+                    if 'resources' in c:
                         itip['resources'] = c['resources']
 
                     itip['raw'] = itip_payload
@@ -127,8 +142,13 @@
                             itip['xml'] = todo_from_ical(c, itip_payload)
                         else:
                             itip['xml'] = event_from_ical(c, itip_payload)
-                    except Exception, e:
-                        log.error("event|todo_from_ical() exception: %r; iCal: %s" % (e, itip_payload))
+
+                    # pylint: disable=broad-except
+                    except Exception as e:
+                        log.error(
+                            "event|todo_from_ical() exception: %r; iCal: %s" % (e, itip_payload)
+                        )
+
                         continue
 
                     itip_objects.append(itip)
@@ -148,6 +168,7 @@
 
     return itip_objects
 
+
 def check_event_conflict(kolab_event, itip_event):
     """
         Determine whether the given kolab event conflicts with the given itip event
@@ -166,14 +187,11 @@
         return conflict
 
     _es = to_dt(kolab_event.get_start())
-    _ee = to_dt(kolab_event.get_ical_dtend())  # use iCal style end date: next day for all-day events
-    _ev = kolab_event
-    _ei = 0
+    # use iCal style end date: next day for all-day events
+    _ee = to_dt(kolab_event.get_ical_dtend())
 
     _is = to_dt(itip_event['start'])
     _ie = to_dt(itip_event['end'])
-    _iv = itip_event['xml']
-    _ii = 0
 
     # Escape looping through anything if neither of the events is recurring.
     if not itip_event['xml'].is_recurring() and not kolab_event.is_recurring():
@@ -193,10 +211,17 @@
         # the older one.
         if _ee < _is:
             while _ee < _is and _es is not None and kolab_event.is_recurring():
-                log.debug("Attempt to move forward kolab event recurrence from %s closer to %s" % (_ee, _is), level=8)
+                log.debug(
+                    "Attempt to move forward kolab event recurrence from {} closer to {}".format(
+                        _ee,
+                        _is
+                    ),
+                    level=8
+                )
+
                 __es = to_dt(kolab_event.get_next_occurence(_es))
 
-                if not __es is None:
+                if __es is not None and not __es == _es:
                     _es = __es
                     _ee = to_dt(kolab_event.get_occurence_end_date(_es))
                 else:
@@ -207,10 +232,17 @@
         # prime spot, this time with the iTip event.
         elif _ie < _es:
             while _ie < _es and _is is not None and itip_event['xml'].is_recurring():
-                log.debug("Attempt to move forward itip event recurrence from %s closer to %s" % (_ie, _es), level=8)
+                log.debug(
+                    "Attempt to move forward itip event recurrence from {} closer to {}".format(
+                        _ie,
+                        _es
+                    ),
+                    level=8
+                )
+
                 __is = to_dt(itip_event['xml'].get_next_occurence(_is))
 
-                if not __is is None:
+                if __is is not None and not _is == __is:
                     _is = __is
                     _ie = to_dt(itip_event['xml'].get_occurence_end_date(_is))
                 else:
@@ -219,7 +251,12 @@
 
         # Now that we have some events somewhere in the same neighborhood...
         conflict = check_date_conflict(_es, _ee, _is, _ie)
-        log.debug("* Comparing itip at %s/%s with kolab at %s/%s: %r (%d)" % (_is, _ie, _es, _ee, conflict, loop), level=8)
+        log.debug(
+            "* Comparing itip at %s/%s with kolab at %s/%s: conflict - %r (occurence - %d)" % (
+                _is, _ie, _es, _ee, conflict, loop
+            ),
+            level=8
+        )
 
         if not conflict:
             if kolab_event.is_recurring() and itip_event['xml'].is_recurring():
@@ -237,9 +274,11 @@
 
     return conflict
 
+
 def _is_transparent(event):
     return event.get_transparency() or event.get_status() == kolabformat.StatusCancelled
 
+
 def _convert_itip_payload(itip):
     matchlist = re.findall("^((DTSTART|DTEND|DUE|EXDATE|COMPLETED)[:;][^\n]+)$", itip, re.MULTILINE)
 
@@ -267,6 +306,7 @@
 
     return itip
 
+
 def check_date_conflict(_es, _ee, _is, _ie):
     """
         Check the given event start/end dates for conflicts
@@ -285,7 +325,7 @@
             conflict = True
     elif _es == _is:
         conflict = True
-    else: # _es > _is
+    else:  # _es > _is
         if _es < _ie:
             conflict = True
         else:
@@ -304,29 +344,47 @@
     smtp = None
 
     if isinstance(itip_events, dict):
-        itip_events = [ itip_events ]
+        itip_events = [itip_events]
 
     for itip_event in itip_events:
         attendee = itip_event['xml'].get_attendee_by_email(from_address)
         participant_status = itip_event['xml'].get_ical_attendee_participant_status(attendee)
 
-        log.debug(_("Send iTip reply %s for %s %r") % (participant_status, itip_event['xml'].type, itip_event['xml'].uid), level=8)
+        log.debug(
+            "Send iTip reply {} for {} {}".format(
+                participant_status,
+                itip_event['xml'].type,
+                itip_event['xml'].uid
+            ),
+            level=8
+        )
 
         event_summary = itip_event['xml'].get_summary()
-        message_text = response_text % { 'summary':event_summary, 'status':participant_status_label(participant_status), 'name':attendee.get_name() }
+        message_text = response_text % {
+            'summary': event_summary,
+            'status': participant_status_label(participant_status),
+            'name': attendee.get_name()
+        }
 
         if subject is not None:
-            subject = subject % { 'summary':event_summary, 'status':participant_status_label(participant_status), 'name':attendee.get_name() }
+            subject = subject % {
+                'summary': event_summary,
+                'status': participant_status_label(participant_status),
+                'name': attendee.get_name()
+            }
 
         try:
-            message = itip_event['xml'].to_message_itip(from_address,
+            message = itip_event['xml'].to_message_itip(
+                from_address,
                 method="REPLY",
                 participant_status=participant_status,
                 message_text=message_text,
                 subject=subject
             )
-        except Exception, e:
-            log.error(_("Failed to compose iTip reply message: %r: %s") % (e, traceback.format_exc()))
+
+        # pylint: disable=broad-except
+        except Exception as e:
+            log.error("Failed to compose iTip reply message: %r: %s" % (e, traceback.format_exc()))
             return
 
         smtp = smtplib.SMTP("localhost", 10026)  # replies go through wallace again
@@ -336,7 +394,9 @@
 
         try:
             smtp.sendmail(message['From'], message['To'], message.as_string())
-        except Exception, e:
+
+        # pylint: disable=broad-except
+        except Exception as e:
             log.error(_("SMTP sendmail error: %r") % (e))
 
     if smtp:
@@ -353,22 +413,25 @@
     smtp = None
 
     if isinstance(itip_events, dict):
-        itip_events = [ itip_events ]
+        itip_events = [itip_events]
 
     for itip_event in itip_events:
         event_summary = itip_event['xml'].get_summary()
-        message_text = request_text % { 'summary':event_summary }
+        message_text = request_text % {'summary': event_summary}
 
         if subject is not None:
-            subject = subject % { 'summary':event_summary }
+            subject = subject % {'summary': event_summary}
 
         try:
-            message = itip_event['xml'].to_message_itip(None,
+            message = itip_event['xml'].to_message_itip(
+                None,
                 method="REQUEST",
                 message_text=message_text,
                 subject=subject
             )
-        except Exception, e:
+
+        # pylint: disable=broad-except
+        except Exception as e:
             log.error(_("Failed to compose iTip request message: %r") % (e))
             return
 
@@ -380,7 +443,9 @@
 
         try:
             smtp.sendmail(message['From'], to_address, message.as_string())
-        except Exception, e:
+
+        # pylint: disable=broad-except
+        except Exception as e:
             log.error(_("SMTP sendmail error: %r") % (e))
 
     if smtp: