diff --git a/ryu/lib/packet/ipv4.py b/ryu/lib/packet/ipv4.py
index 2adf6895..21d227ad 100644
--- a/ryu/lib/packet/ipv4.py
+++ b/ryu/lib/packet/ipv4.py
@@ -62,7 +62,7 @@ class ipv4(packet_base.PacketBase):
         return msg, ipv4.get_packet_type(proto)
 
     def serialize(self, payload, prev):
-        hdr = bytearray().zfill(self.header_length * 4)
+        hdr = bytearray(self.header_length * 4)
         version = self.version << 4 | self.header_length
         flags = self.flags << 13 | self.offset
         if self.total_length == 0:
diff --git a/ryu/lib/packet/tcp.py b/ryu/lib/packet/tcp.py
index ec177f03..81c79336 100644
--- a/ryu/lib/packet/tcp.py
+++ b/ryu/lib/packet/tcp.py
@@ -54,7 +54,7 @@ class tcp(packet_base.PacketBase):
         return msg, None
 
     def serialize(self, payload, prev):
-        h = bytearray().zfill(self.length)
+        h = bytearray(self.length)
         offset = self.offset << 4
         struct.pack_into(tcp._PACK_STR, h, 0, self.src_port, self.dst_port,
                          self.seq, self.ack, offset, self.bits,
@@ -69,7 +69,7 @@ class tcp(packet_base.PacketBase):
             ph = struct.pack('!IIBBH', prev.src, prev.dst, 0, 6, length)
             f = ph + h + payload
             if len(f) % 2:
-                f += '\0'
+                f += '\x00'
             self.csum = socket.htons(packet_utils.checksum(f))
             struct.pack_into('!H', h, 16, self.csum)
         return h
diff --git a/ryu/lib/packet/udp.py b/ryu/lib/packet/udp.py
index 2b858d98..b949b5ca 100644
--- a/ryu/lib/packet/udp.py
+++ b/ryu/lib/packet/udp.py
@@ -47,7 +47,7 @@ class udp(packet_base.PacketBase):
             ph = struct.pack('!IIBBH', prev.src, prev.dst, 0, 17, self.length)
             f = ph + h + payload
             if len(f) % 2:
-                f += '\0'
+                f += '\x00'
             self.csum = socket.htons(packet_utils.checksum(f))
             h = struct.pack(udp._PACK_STR, self.src_port, self.dst_port,
                             self.length, self.csum)
diff --git a/ryu/ofproto/ofproto_parser.py b/ryu/ofproto/ofproto_parser.py
index 21a86a9f..26adead6 100644
--- a/ryu/ofproto/ofproto_parser.py
+++ b/ryu/ofproto/ofproto_parser.py
@@ -93,7 +93,7 @@ class MsgBase(object):
 
         self.version = self.datapath.ofproto.OFP_VERSION
         self.msg_type = self.cls_msg_type
-        self.buf = bytearray().zfill(self.datapath.ofproto.OFP_HEADER_SIZE)
+        self.buf = bytearray(self.datapath.ofproto.OFP_HEADER_SIZE)
 
     def _serialize_header(self):
         # buffer length is determined after trailing data is formated.
@@ -122,7 +122,7 @@ class MsgBase(object):
 
 def msg_pack_into(fmt, buf, offset, *args):
     if len(buf) < offset:
-        buf += bytearray().zfill(offset - len(buf))
+        buf += bytearray(offset - len(buf))
 
     if len(buf) == offset:
         buf += struct.pack(fmt, *args)
@@ -130,7 +130,7 @@ def msg_pack_into(fmt, buf, offset, *args):
 
     needed_len = offset + struct.calcsize(fmt)
     if len(buf) < needed_len:
-        buf += bytearray().zfill(needed_len - len(buf))
+        buf += bytearray(needed_len - len(buf))
 
     struct.pack_into(fmt, buf, offset, *args)
 
diff --git a/ryu/tests/unit/ofproto/test_ofproto_parser.py b/ryu/tests/unit/ofproto/test_ofproto_parser.py
index 114a6998..9baf46ab 100644
--- a/ryu/tests/unit/ofproto/test_ofproto_parser.py
+++ b/ryu/tests/unit/ofproto/test_ofproto_parser.py
@@ -252,7 +252,7 @@ class TestMsgPackInto(unittest.TestCase):
     def _test_msg_pack_into(self, offset_type='e'):
         fmt = '!HH'
         len_ = struct.calcsize(fmt)
-        buf = bytearray().zfill(len_)
+        buf = bytearray(len_)
         offset = len_
         arg1 = 1
         arg2 = 2