diff --git a/src/genpy/dynamic.py b/src/genpy/dynamic.py
index da314b3..5b0efff 100644
--- a/src/genpy/dynamic.py
+++ b/src/genpy/dynamic.py
@@ -161,7 +161,7 @@ def generate_dynamic(core_type, msg_cat):
     
     # write the entire text to a file and import it (it will get deleted when tmp_dir goes - above)
     tmp_file = tempfile.NamedTemporaryFile(suffix=".py",dir=tmp_dir,delete=False)
-    tmp_file.file.write(full_text)
+    tmp_file.file.write(full_text.encode())
     tmp_file.file.close()
 
     # import our temporary file as a python module, which requires modifying sys.path
diff --git a/src/genpy/generator.py b/src/genpy/generator.py
index cd36811..9d8a421 100644
--- a/src/genpy/generator.py
+++ b/src/genpy/generator.py
@@ -429,7 +429,10 @@ def string_serializer_generator(package, type_, name, serialize):
             yield INDENT+"%s = %s.encode('utf-8')"%(var,var) #For unicode-strings in Python2, encode using utf-8
             yield INDENT+"length = len(%s)"%(var) # Update the length after utf-8 conversion
 
-            yield pack2("'<I%ss'%length", "length, %s"%var)
+            yield "if python3:"
+            yield INDENT+pack2("'<I%sB'%length", "length, *%s"%var)
+            yield "else:"
+            yield INDENT+pack2("'<I%ss'%length", "length, %s"%var)
     else:
         yield "start = end"
         if array_len is not None:
diff --git a/src/genpy/message.py b/src/genpy/message.py
index 8aef330..b18402f 100644
--- a/src/genpy/message.py
+++ b/src/genpy/message.py
@@ -201,7 +201,12 @@ def check_type(field_name, field_type, field_val):
     elif field_type == 'string':
         if sys.hexversion > 0x03000000:
             if type(field_val) == str:
-                raise SerializationError('field %s is a unicode string instead of an ascii string'%field_name)	
+                try:
+                    field_val.encode('ascii')
+                except UnicodeEncodeError:
+                    raise SerializationError('field %s is a non-ascii string'%field_name)
+            elif not type(field_val) == bytes:
+                raise SerializationError('field %s must be of type bytes or an ascii string'%field_name)
         else:		
             if type(field_val) == unicode:
                 raise SerializationError('field %s is a unicode string instead of an ascii string'%field_name)
diff --git a/src/genpy/rostime.py b/src/genpy/rostime.py
index ae7ad5e..1c8326e 100644
--- a/src/genpy/rostime.py
+++ b/src/genpy/rostime.py
@@ -120,9 +120,15 @@ def __str__(self):
     def __repr__(self):
         return "genpy.TVal[%d]"%self.to_nsec()
 
+    def __bool__(self):
+        """
+        Return if time value is not zero
+        """
+        return self.secs != 0 or self.nsecs != 0
+
     def __nonzero__(self):
         """
-        Check if time value is zero
+        Check if time value is not zero
         """
         return self.secs or self.nsecs
 
@@ -278,6 +284,9 @@ def __eq__(self, other):
             return False
         return self.secs == other.secs and self.nsecs == other.nsecs
 
+    def __hash__(self):
+        return super(Time, self).__hash__()
+
 class Duration(TVal):
     """
     Duration represents the ROS 'duration' primitive, which consists
@@ -429,3 +438,6 @@ def __eq__(self, other):
         if not isinstance(other, Duration):
             return False
         return self.secs == other.secs and self.nsecs == other.nsecs
+
+    def __hash__(self):
+        return super(Duration, self).__hash__()
diff --git a/test/files/array/string_fixed_ser.txt b/test/files/array/string_fixed_ser.txt
index f539625..bc8ae8c 100644
--- a/test/files/array/string_fixed_ser.txt
+++ b/test/files/array/string_fixed_ser.txt
@@ -3,4 +3,7 @@ for val0 in data:
   if python3 or type(val0) == unicode:
     val0 = val0.encode('utf-8')
     length = len(val0)
-  buff.write(struct.pack('<I%ss'%length, length, val0))
+  if python3:
+    buff.write(struct.pack('<I%sB'%length, length, *val0))
+  else:
+    buff.write(struct.pack('<I%ss'%length, length, val0))
diff --git a/test/files/array/string_varlen_ser.txt b/test/files/array/string_varlen_ser.txt
index 252ae7a..d360c5a 100644
--- a/test/files/array/string_varlen_ser.txt
+++ b/test/files/array/string_varlen_ser.txt
@@ -5,4 +5,7 @@ for val0 in data:
   if python3 or type(val0) == unicode:
     val0 = val0.encode('utf-8')
     length = len(val0)
-  buff.write(struct.pack('<I%ss'%length, length, val0))
+  if python3:
+    buff.write(struct.pack('<I%sB'%length, length, *val0))
+  else:
+    buff.write(struct.pack('<I%ss'%length, length, val0))
diff --git a/test/test_genpy_dynamic.py b/test/test_genpy_dynamic.py
index b42a8b4..94a5148 100644
--- a/test/test_genpy_dynamic.py
+++ b/test/test_genpy_dynamic.py
@@ -30,20 +30,38 @@
 # ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 # POSSIBILITY OF SUCH DAMAGE.
 
-import cStringIO
+try:
+    from cStringIO import StringIO
+except ImportError:
+    from io import BytesIO as StringIO
+import sys
 import time
 
 def test_generate_dynamic():
     import genpy
     from genpy.dynamic import generate_dynamic
     msgs = generate_dynamic("gd_msgs/EasyString", "string data\n")
-    assert ['gd_msgs/EasyString'] == msgs.keys()
+    assert ['gd_msgs/EasyString'] == list(msgs.keys())
     m_cls = msgs['gd_msgs/EasyString']
     m_instance = m_cls()
     m_instance.data = 'foo'
-    buff = cStringIO.StringIO()
+    buff = StringIO()
     m_instance.serialize(buff)
-    m_cls().deserialize(buff.getvalue())
+    m_instance2 = m_cls().deserialize(buff.getvalue())
+    assert m_instance == m_instance2
+
+    try:
+        char = unichr
+    except NameError:
+        char = chr
+    m_instance.data = 'foo' + char(1234)
+    buff = StringIO()
+    m_instance.serialize(buff)
+    m_instance2 = m_cls().deserialize(buff.getvalue())
+    if sys.hexversion < 0x03000000:
+        # python 2 requires manual decode into unicode
+        m_instance2.data = m_instance2.data.decode('utf-8')
+    assert m_instance == m_instance2
 
     # 'probot_msgs' is a test for #1183, failure if the package no longer exists
     msgs = generate_dynamic("gd_msgs/MoveArmState", """Header header
@@ -102,7 +120,7 @@ def test_generate_dynamic():
     m_instance1 = msgs['probot_msgs/ControllerStatus']()
     m_instance2 = msgs['probot_msgs/ControllerStatus'](value=4, comment=str(time.time()))
     d = {'UNDEFINED':0,'SUCCESS':1,'ABORTED':2,'PREEMPTED':3,'ACTIVE':4}
-    for k, v in d.iteritems():
+    for k, v in d.items():
         assert v == getattr(m_instance1, k)
     _test_ser_deser(m_instance2, m_instance1)
 
@@ -124,7 +142,7 @@ def test_generate_dynamic():
     _test_ser_deser(m_instance2, m_instance1)
 
 def _test_ser_deser(m_instance1, m_instance2):
-    buff = cStringIO.StringIO()
+    buff = StringIO()
     m_instance1.serialize(buff)
     m_instance2.deserialize(buff.getvalue())
     assert m_instance1 == m_instance2
diff --git a/test/test_genpy_generator.py b/test/test_genpy_generator.py
index 1f8b8f8..a6e10be 100644
--- a/test/test_genpy_generator.py
+++ b/test/test_genpy_generator.py
@@ -296,7 +296,10 @@ def test_string_serializer_generator():
 if python3 or type(var_name) == unicode:
   var_name = var_name.encode('utf-8')
   length = len(var_name)
-buff.write(struct.pack('<I%ss'%length, length, var_name))""" == val, val
+if python3:
+  buff.write(struct.pack('<I%sB'%length, length, *var_name))
+else:
+  buff.write(struct.pack('<I%ss'%length, length, var_name))""" == val, val
 
     for t in ['uint8[]', 'byte[]', 'uint8[10]', 'byte[20]']:
         g = genpy.generator.string_serializer_generator('foo', 'uint8[]', 'b_name', True)
diff --git a/test/test_genpy_message.py b/test/test_genpy_message.py
index 64c82d9..89002a5 100644
--- a/test/test_genpy_message.py
+++ b/test/test_genpy_message.py
@@ -30,6 +30,7 @@
 # ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 # POSSIBILITY OF SUCH DAMAGE.
 
+import sys
 import time
 import unittest
 import traceback
@@ -213,7 +214,7 @@ def test_fill_message_args_embed_time(self):
             m = TestFillEmbedTime()            
             try:
                 fill_message_args(m, test)
-            except Exception, e:
+            except Exception as e:
                 self.fail("failed to fill with : %s\n%s"%(str(test), traceback.format_exc()))
 
             self.assertEquals(m.t, Time(10, 20))
@@ -389,15 +390,22 @@ def test_check_types_invalid(self):
                           'test', 'bool', -2)
         self.assertRaises(SerializationError, genpy.message.check_type,
                           'test', 'bool', 2)
+        try:
+            u = unichr(1234)
+        except NameError:
+            u = chr(1234)
         self.assertRaises(SerializationError, genpy.message.check_type,
-                          'test', 'string', u'UnicodeString')
+                          'test', 'string', u)
         
     def test_Message(self):
-        import cStringIO
+        try:
+            from cStringIO import StringIO
+        except ImportError:
+            from io import StringIO
         from genpy import Message, SerializationError
         self.assert_(isinstance(Message(), Message))
         m = Message()
-        b = cStringIO.StringIO()
+        b = StringIO()
         m.serialize(b)
         m.deserialize('')
 
@@ -560,14 +568,17 @@ def __init__(self, t, d):
   nsecs: 456""", strify_message(M5(Time(987, 654), Duration(123, 456))))
         
         # test final clause of strify -- str anything that isn't recognized
-        self.assertEquals("set([1])", strify_message(set([1])))
+        if sys.hexversion > 0x03000000:  # Python3
+            self.assertEquals("{1}", strify_message(set([1])))
+        else:
+            self.assertEquals("set([1])", strify_message(set([1])))
 
     def test_strify_yaml(self):
         def roundtrip(m):
             yaml_text = strify_message(m)
-            print yaml_text
+            print(yaml_text)
             loaded = yaml.load(yaml_text) 
-            print "loaded", loaded
+            print("loaded", loaded)
             new_inst = m.__class__()
             if loaded is not None:
                 fill_message_args(new_inst, [loaded])
@@ -629,7 +640,7 @@ def test_check_type(self):
         for t, v in valids:
             try:
                 check_type('n', t, v)
-            except Exception, e:
+            except Exception as e:
                 traceback.print_exc()
                 raise Exception("failure type[%s] value[%s]: %s"%(t, v, str(e)))