diff --git a/regroup/__init__.py b/regroup/__init__.py
index f82c1d9..5db08d8 100644
--- a/regroup/__init__.py
+++ b/regroup/__init__.py
@@ -19,7 +19,7 @@ def match(strings):
     return DAWG.from_iter(strings).serialize()
 
 
-class StringSet:
+class StringSet(object):
 
     '''
     a set of strings
@@ -35,7 +35,7 @@ def __iter__(self):
         return iter(self.strings.keys())
 
 
-class TaggedString:
+class TaggedString(object):
 
     def __init__(self, string, tokenizer=None):
         tokenizer = tokenizer or Tokenizer()
@@ -51,7 +51,7 @@ def escape(s):
     return re.escape(s).replace(r'\ ', ' ')
 
 
-class Trie:
+class Trie(object):
 
     '''
     Trie
@@ -99,7 +99,7 @@ def _build(self, strings):
         return root
 
 
-class DAWG:
+class DAWG(object):
 
     '''
     Directed Acyclic Word Graph
@@ -109,6 +109,7 @@ class DAWG:
 
     def __init__(self, trie=None):
         self.dawg = DAWG._build(trie)
+        self.trie = trie
 
     @classmethod
     def from_iter(cls, strings):
@@ -167,7 +168,8 @@ def flatten(d, clusters=None):
     def _flatten(cls, d, path):
         for k, v in sorted(d.items()):
             if k:
-                yield from cls._flatten(v, path + k)
+                for item in cls._flatten(v, path + k):
+                    yield item
             else:
                 yield path
 
@@ -193,18 +195,18 @@ def _cluster_by_prefixlen(cls, length, clusters, d, path):
             else:
                 cls._cluster_by_prefixlen(length, clusters, v, path2)
 
-    def dawg_weights(d, l):
+    def dawg_weights(self, d, l):
         """given a DAWG and the original list, calculate weights at each branchpoint"""
         weights = defaultdict(int)
-        _dawg_weights(l, weights, d, [])
+        self._dawg_weights(l, weights, d, [])
         return dict(weights)
 
-    def _dawg_weights(l, weights, d, path):
+    def _dawg_weights(self, l, weights, d, path):
         for k, v in d.items():
             path2 = path + [k]
             path2str = ''.join(path)
             weights[tuple(path2)] += sum(1 for x in l if x.startswith(path2str))
-            _dawg_weights(l, weights, v, path2)
+            self._dawg_weights(l, weights, v, path2)
 
     def top_weights(weights, n):
         wsorted = sorted(weights.items(),
@@ -329,7 +331,7 @@ def as_optional_group(strings):
 
 
 def all_len01(l):
-    return set(map(len, l)) == {0, 1}
+    return set(map(len, l)) == set([0, 1])
 
 
 def is_optional_char_class(d):
@@ -484,7 +486,8 @@ def _relaxable(cls, d):
             yield (diffcnt, d)
         for k, v in d.items():
             if len(v) > 1:
-                yield from cls._relaxable(v)
+                for item in cls._relaxable(v):
+                    yield item
 
     def relax(self, threshold=1):
         '''
@@ -503,7 +506,7 @@ def relax(self, threshold=1):
 
     def do_relax(self, d):
         merged = reduce(dict_merge, d.values(), {})
-        d2 = {k: merged for k in d}
+        d2 = dict([(k, merged) for k in d])
         # print('merged', merged)
         # print('d2', d2)
         return DAWGRelaxer._replace(self.dawg.dawg, d, d2)
@@ -512,5 +515,4 @@ def do_relax(self, d):
     def _replace(cls, dawg, find, replace):
         if dawg == find:
             return replace
-        return {k: cls._replace(v, find, replace)
-                for k, v in dawg.items()}
+        return dict([(k, cls._replace(v, find, replace)) for k, v in dawg.items()])
diff --git a/regroup/cluster.py b/regroup/cluster.py
index d08ee7e..d921aee 100644
--- a/regroup/cluster.py
+++ b/regroup/cluster.py
@@ -1,12 +1,17 @@
 
+import re
 
-class Cluster:
+class Cluster(object):
     def __init__(self):
         self.left = None
         self.dist = None
         self.right = None
+        
+        
     def __repr__(self):
         return '({} {} {})'.format(self.left, self.dist, self.right)
+    
+    
     def dump(self, indent=0):
         if isinstance(self.left, str):
             print(' ' * indent, self.left)
@@ -17,33 +22,49 @@ def dump(self, indent=0):
             print(' ' * indent, self.right)
         else:
             self.right.dump(indent=indent+1)
+            
+            
     def __iter__(self):
         yield self
         if self.left:
-            yield from self.left
+            for item in self.left:
+                yield item
         if self.right:
-            yield from self.right
+            for item in self.right:
+                yield item
+            
+            
     def leaves(self):
         if isinstance(self.left, str):
             yield self.left
         else:
-            yield from self.left.leaves()
+            for item in self.left.leaves():
+                yield item
         if isinstance(self.right, str):
             yield self.right
         else:
-            yield from self.right.leaves()
+            for item in self.right.leaves():
+                yield item
+            
+            
     def distances(self):
         yield self.dist
         if isinstance(self.left, Cluster):
-            yield from self.left.distances()
+            for item in self.left.distances():
+                yield item
         if isinstance(self.right, Cluster):
-            yield from self.right.distances()
+            for item in self.right.distances():
+                yield item
+            
+            
     def clusters_by(self, dist):
         if self.dist <= dist:
             return list(self.leaves())
         else:
             return (self.left.clusters_by(dist),
                     self.right.clusters_by(dist))
+        
+        
     def add(self, clusters, grid, lefti, righti):
         self.left = clusters[lefti]
         self.right = clusters[righti]
@@ -77,6 +98,7 @@ def agglomerate(labels, grid):
 
 
 def strdist(x, y):
+    #TODO: function levenshtein never got imported or defined
     return levenshtein(x, y)
     
 
diff --git a/regroup/tokenizer.py b/regroup/tokenizer.py
index 40cc879..7dc610b 100644
--- a/regroup/tokenizer.py
+++ b/regroup/tokenizer.py
@@ -14,7 +14,7 @@ def tokenize_regex_case_sensitive(string):
         yield token
 
 
-class Tokenizer:
+class Tokenizer(object):
 
     def __init__(self):
         pass
@@ -26,6 +26,7 @@ def tokenize(self, string):
 class DictionaryTokenizer(Tokenizer):
 
     def __init__(self, wordset=None):
+        Tokenizer.__init__(self)
         wordset = set(wordset) if wordset else set()
         self.wordset = wordset
         self.wordsetlen = defaultdict(set)
@@ -58,7 +59,7 @@ def fallback(self, string):
         return string[0]
 
 
-class Tagged:
+class Tagged(object):
 
     def __init__(self, string, tag):
         self.string = string
@@ -68,7 +69,7 @@ def __str__(self):
         return self.string
 
 
-class TaggingTokenizer:
+class TaggingTokenizer(object):
 
     def __init__(self, tags):
         self.tags = tags