diff --git a/offlineimap/utils/stacktrace.py b/offlineimap/utils/stacktrace.py
index eacd5e8..c9a4826 100644
--- a/offlineimap/utils/stacktrace.py
+++ b/offlineimap/utils/stacktrace.py
@@ -12,14 +12,15 @@ import traceback
 def dump(out):
     """ Dumps current stack trace into I/O object 'out' """
     id2name = {}
-    for th in threading.enumerate():
-        id2name[th.ident] = th.name
-    n = 0
+    for th_en in threading.enumerate():
+        id2name[th_en.ident] = th_en.name
+
+    count = 0
     for i, stack in list(sys._current_frames().items()):
-        out.write("\n# Thread #%d (id=%d), %s\n" % (n, i, id2name[i]))
-        n = n + 1
-        for f, lno, name, line in traceback.extract_stack(stack):
-            out.write('File: "%s", line %d, in %s' % (f, lno, name))
+        out.write("\n# Thread #%d (id=%d), %s\n" % (count, i, id2name[i]))
+        count = count + 1
+        for file, lno, name, line in traceback.extract_stack(stack):
+            out.write('File: "%s", line %d, in %s' % (file, lno, name))
             if line:
                 out.write(" %s" % (line.strip()))
             out.write("\n")