diff --git a/offlineimap/folder/IMAP.py b/offlineimap/folder/IMAP.py
index 0bbe746..d06c740 100644
--- a/offlineimap/folder/IMAP.py
+++ b/offlineimap/folder/IMAP.py
@@ -186,7 +186,7 @@ class IMAPFolder(BaseFolder):
                 continue
             messagestr = messagestr.split(' ', 1)[1]
             options = imaputil.flags2hash(messagestr)
-            if not options.has_key('UID'):
+            if not 'UID' in options:
                 self.ui.warn('No UID in message with options %s' %\
                                           str(options),
                                           minor = 1)
diff --git a/offlineimap/folder/UIDMaps.py b/offlineimap/folder/UIDMaps.py
index 36e92af..f306459 100644
--- a/offlineimap/folder/UIDMaps.py
+++ b/offlineimap/folder/UIDMaps.py
@@ -94,7 +94,7 @@ class MappedIMAPFolder(IMAPFolder):
             # summary that have been deleted from the folder.
 
             for luid in self.diskl2r.keys():
-                if not reallist.has_key(luid):
+                if not luid in reallist:
                     ruid = self.diskl2r[luid]
                     del self.diskr2l[ruid]
                     del self.diskl2r[luid]
@@ -107,7 +107,7 @@ class MappedIMAPFolder(IMAPFolder):
             self.l2r = self.diskl2r.copy()
 
             for luid in reallist.keys():
-                if not self.l2r.has_key(luid):
+                if not luid in self.l2r:
                     ruid = nextneg
                     nextneg -= 1
                     self.l2r[luid] = ruid
diff --git a/offlineimap/imaplibutil.py b/offlineimap/imaplibutil.py
index 2d5fc39..2aa81d9 100644
--- a/offlineimap/imaplibutil.py
+++ b/offlineimap/imaplibutil.py
@@ -137,7 +137,7 @@ class WrappedIMAP4_SSL(UsefulIMAPMixIn, IMAP4_SSL):
     """Improved version of imaplib.IMAP4_SSL overriding select()"""
     def __init__(self, *args, **kwargs):
         self._fingerprint = kwargs.get('fingerprint', None)
-        if kwargs.has_key('fingerprint'):
+        if 'fingerprint' in kwargs:
             del kwargs['fingerprint']
         super(WrappedIMAP4_SSL, self).__init__(*args, **kwargs)
 
diff --git a/offlineimap/threadutil.py b/offlineimap/threadutil.py
index 054fa11..a29e68f 100644
--- a/offlineimap/threadutil.py
+++ b/offlineimap/threadutil.py
@@ -209,7 +209,7 @@ def initInstanceLimit(instancename, instancemax):
     """Initialize the instance-limited thread implementation to permit
     up to intancemax threads with the given instancename."""
     instancelimitedlock.acquire()
-    if not instancelimitedsems.has_key(instancename):
+    if not instancename in instancelimitedsems:
         instancelimitedsems[instancename] = BoundedSemaphore(instancemax)
     instancelimitedlock.release()
 
diff --git a/offlineimap/ui/UIBase.py b/offlineimap/ui/UIBase.py
index bf46e6f..a8aeeaf 100644
--- a/offlineimap/ui/UIBase.py
+++ b/offlineimap/ui/UIBase.py
@@ -159,7 +159,7 @@ class UIBase(object):
 
     def unregisterthread(self, thr):
         """Unregister a thread as being associated with an account name"""
-        if self.threadaccounts.has_key(thr):
+        if thr in self.threadaccounts:
             del self.threadaccounts[thr]
         self.debug('thread', "Unregister thread '%s'" % thr.getName())
 
@@ -175,7 +175,7 @@ class UIBase(object):
 
     def debug(self, debugtype, msg):
         cur_thread = threading.currentThread()
-        if not self.debugmessages.has_key(cur_thread):
+        if not cur_thread in self.debugmessages:
             # deque(..., self.debugmsglen) would be handy but was
             # introduced in p2.6 only, so we'll need to work around and
             # shorten our debugmsg list manually :-(
@@ -403,7 +403,7 @@ class UIBase(object):
     ################################################## Threads
 
     def getThreadDebugLog(self, thread):
-        if self.debugmessages.has_key(thread):
+        if thread in self.debugmessages:
             message = "\nLast %d debug messages logged for %s prior to exception:\n"\
                        % (len(self.debugmessages[thread]), thread.getName())
             message += "\n".join(self.debugmessages[thread])