fixes for mutable default arguments

modify the default argument from list to None,
because default value {}/[] as argument is dangerous.

Signed-off-by: Minoru TAKAHASHI <takahashi.minoru7@gmail.com>
Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>

11 files changed, 124 insertions, 61 deletions

diff --git a/ryu/lib/bfdlib.py b/ryu/lib/bfdlib.py
index c3e1973d..388618a7 100644
--- a/ryu/lib/bfdlib.py
+++ b/ryu/lib/bfdlib.py
@@ -78,7 +78,7 @@ class BFDSession(object):
                  detect_mult=3,
                  desired_min_tx_interval=1000000,
                  required_min_rx_interval=1000000,
-                 auth_type=0, auth_keys={}):
+                 auth_type=0, auth_keys=None):
         """
         Initialize a BFD session.
 
@@ -128,6 +128,7 @@ class BFDSession(object):
                               auth_keys={1: "secret key 1",
                                          2: "secret key 2"})
         """
+        auth_keys = auth_keys if auth_keys else {}
         assert not (auth_type and len(auth_keys) == 0)
 
         # RyuApp reference to BFDLib
@@ -787,7 +788,7 @@ class BFDLib(app_manager.RyuApp):
 
     def add_bfd_session(self, dpid, ofport, src_mac, src_ip,
                         dst_mac="FF:FF:FF:FF:FF:FF", dst_ip="255.255.255.255",
-                        auth_type=0, auth_keys={}):
+                        auth_type=0, auth_keys=None):
         """
         Establish a new BFD session and return My Discriminator of new session.
 
@@ -822,6 +823,7 @@ class BFDLib(app_manager.RyuApp):
                             auth_keys={1: "secret key 1",
                                        2: "secret key 2"})
         """
+        auth_keys = auth_keys if auth_keys else {}
         # Generate a unique discriminator
         while True:
             # Generate My Discriminator
diff --git a/ryu/lib/ovs/bridge.py b/ryu/lib/ovs/bridge.py
index 92dc28b6..02b9acb3 100644
--- a/ryu/lib/ovs/bridge.py
+++ b/ryu/lib/ovs/bridge.py
@@ -261,7 +261,8 @@ class OVSBridge(object):
             return command.result[0]
         return None
 
-    def set_qos(self, port_name, type='linux-htb', max_rate=None, queues=[]):
+    def set_qos(self, port_name, type='linux-htb', max_rate=None, queues=None):
+        queues = queues if queues else []
         command_qos = ovs_vsctl.VSCtlCommand(
             'set-qos',
             [port_name, type, max_rate])
diff --git a/ryu/lib/packet/bfd.py b/ryu/lib/packet/bfd.py
index e12fec5d..61c7943c 100644
--- a/ryu/lib/packet/bfd.py
+++ b/ryu/lib/packet/bfd.py
@@ -417,7 +417,7 @@ class SimplePassword(BFDAuth):
         return self.serialize_hdr() + \
             struct.pack(self._PACK_STR, self.auth_key_id) + self.password
 
-    def authenticate(self, prev=None, auth_keys={}):
+    def authenticate(self, prev=None, auth_keys=None):
         """Authenticate the password for this packet.
 
         This method can be invoked only when ``self.password`` is defined.
@@ -431,6 +431,7 @@ class SimplePassword(BFDAuth):
         ``auth_keys`` is a dictionary of authentication key chain which
         key is an integer of *Auth Key ID* and value is a string of *Password*.
         """
+        auth_keys = auth_keys if auth_keys else {}
         assert isinstance(prev, bfd)
         if self.auth_key_id in auth_keys and \
                 self.password == auth_keys[self.auth_key_id]:
@@ -520,7 +521,7 @@ class KeyedMD5(BFDAuth):
         return auth_hdr_bin + struct.pack(self._PACK_STR, self.auth_key_id, 0,
                                           self.seq, self.digest)
 
-    def authenticate(self, prev, auth_keys={}):
+    def authenticate(self, prev, auth_keys=None):
         """Authenticate the MD5 digest for this packet.
 
         This method can be invoked only when ``self.digest`` is defined.
@@ -536,6 +537,7 @@ class KeyedMD5(BFDAuth):
         ``auth_keys`` is a dictionary of authentication key chain which
         key is an integer of *Auth Key ID* and value is a string of *Auth Key*.
         """
+        auth_keys = auth_keys if auth_keys else {}
         assert isinstance(prev, bfd)
 
         if self.digest is None:
@@ -670,7 +672,7 @@ class KeyedSHA1(BFDAuth):
         return auth_hdr_bin + struct.pack(self._PACK_STR, self.auth_key_id, 0,
                                           self.seq, self.auth_hash)
 
-    def authenticate(self, prev, auth_keys={}):
+    def authenticate(self, prev, auth_keys=None):
         """Authenticate the SHA1 hash for this packet.
 
         This method can be invoked only when ``self.auth_hash`` is defined.
@@ -686,6 +688,7 @@ class KeyedSHA1(BFDAuth):
         ``auth_keys`` is a dictionary of authentication key chain which
         key is an integer of *Auth Key ID* and value is a string of *Auth Key*.
         """
+        auth_keys = auth_keys if auth_keys else {}
         assert isinstance(prev, bfd)
 
         if self.auth_hash is None:
diff --git a/ryu/lib/packet/bgp.py b/ryu/lib/packet/bgp.py
index 66dbc3c7..cad43806 100644
--- a/ryu/lib/packet/bgp.py
+++ b/ryu/lib/packet/bgp.py
@@ -780,7 +780,8 @@ class _LabelledAddrPrefix(_AddrPrefix):
     #
     _WITHDRAW_LABEL = 0x800000
 
-    def __init__(self, length, addr, labels=[], **kwargs):
+    def __init__(self, length, addr, labels=None, **kwargs):
+        labels = labels if labels else []
         assert isinstance(labels, list)
         is_tuple = isinstance(addr, tuple)
         if is_tuple:
@@ -2246,8 +2247,9 @@ class BGPOpen(BGPMessage):
     }
 
     def __init__(self, my_as, bgp_identifier, type_=BGP_MSG_OPEN,
-                 opt_param_len=0, opt_param=[],
+                 opt_param_len=0, opt_param=None,
                  version=_VERSION, hold_time=0, len_=None, marker=None):
+        opt_param = opt_param if opt_param else []
         super(BGPOpen, self).__init__(marker=marker, len_=len_, type_=type_)
         self.version = version
         self.my_as = my_as
@@ -2332,11 +2334,14 @@ class BGPUpdate(BGPMessage):
 
     def __init__(self, type_=BGP_MSG_UPDATE,
                  withdrawn_routes_len=None,
-                 withdrawn_routes=[],
+                 withdrawn_routes=None,
                  total_path_attribute_len=None,
-                 path_attributes=[],
-                 nlri=[],
+                 path_attributes=None,
+                 nlri=None,
                  len_=None, marker=None):
+        withdrawn_routes = withdrawn_routes if withdrawn_routes else []
+        path_attributes = path_attributes if path_attributes else []
+        nlri = nlri if nlri else []
         super(BGPUpdate, self).__init__(marker=marker, len_=len_, type_=type_)
         self.withdrawn_routes_len = withdrawn_routes_len
         self.withdrawn_routes = withdrawn_routes
diff --git a/ryu/lib/packet/ospf.py b/ryu/lib/packet/ospf.py
index 0cc20267..98c5d71c 100644
--- a/ryu/lib/packet/ospf.py
+++ b/ryu/lib/packet/ospf.py
@@ -280,7 +280,8 @@ class RouterLSA(LSA):
 
     def __init__(self, ls_age=0, options=0, type_=OSPF_ROUTER_LSA,
                  id_='0.0.0.0', adv_router='0.0.0.0', ls_seqnum=0,
-                 checksum=None, length=None, flags=0, links=[]):
+                 checksum=None, length=None, flags=0, links=None):
+        links = links if links else []
         self.flags = flags
         self.links = links
         super(RouterLSA, self).__init__(ls_age, options, type_, id_,
@@ -320,7 +321,8 @@ class NetworkLSA(LSA):
 
     def __init__(self, ls_age=0, options=0, type_=OSPF_NETWORK_LSA,
                  id_='0.0.0.0', adv_router='0.0.0.0', ls_seqnum=0,
-                 checksum=None, length=None, mask='0.0.0.0', routers=[]):
+                 checksum=None, length=None, mask='0.0.0.0', routers=None):
+        routers = routers if routers else []
         self.mask = mask
         self.routers = routers
         super(NetworkLSA, self).__init__(ls_age, options, type_, id_,
@@ -439,7 +441,8 @@ class ASExternalLSA(LSA):
 
     def __init__(self, ls_age=0, options=0, type_=OSPF_AS_EXTERNAL_LSA,
                  id_='0.0.0.0', adv_router='0.0.0.0', ls_seqnum=0,
-                 checksum=None, length=None, extnws=[]):
+                 checksum=None, length=None, extnws=None):
+        extnws = extnws if extnws else []
         self.extnws = extnws
         super(ASExternalLSA, self).__init__(ls_age, options, type_, id_,
                                             adv_router, ls_seqnum, checksum,
@@ -539,7 +542,8 @@ class PrefixSIDSubTLV(ExtendedPrefixTLV):
 
 
 class OpaqueBody(StringifyMixin, _TypeDisp):
-    def __init__(self, tlvs=[]):
+    def __init__(self, tlvs=None):
+        tlvs = tlvs if tlvs else []
         self.tlvs = tlvs
 
     def serialize(self):
@@ -718,7 +722,8 @@ class OSPFHello(OSPFMessage):
                  au_type=1, authentication=0, checksum=None, version=_VERSION,
                  mask='0.0.0.0', hello_interval=10, options=0, priority=1,
                  dead_interval=40, designated_router='0.0.0.0',
-                 backup_router='0.0.0.0', neighbors=[]):
+                 backup_router='0.0.0.0', neighbors=None):
+        neighbors = neighbors if neighbors else []
         super(OSPFHello, self).__init__(OSPF_MSG_HELLO, length, router_id,
                                         area_id, au_type, authentication,
                                         checksum, version)
@@ -782,7 +787,8 @@ class OSPFDBDesc(OSPFMessage):
     def __init__(self, length=None, router_id='0.0.0.0', area_id='0.0.0.0',
                  au_type=1, authentication=0, checksum=None, version=_VERSION,
                  mtu=1500, options=0, i_flag=0, m_flag=0, ms_flag=0,
-                 sequence_number=0, lsa_headers=[]):
+                 sequence_number=0, lsa_headers=None):
+        lsa_headers = lsa_headers if lsa_headers else []
         super(OSPFDBDesc, self).__init__(OSPF_MSG_DB_DESC, length, router_id,
                                          area_id, au_type, authentication,
                                          checksum, version)
@@ -865,7 +871,8 @@ class OSPFLSReq(OSPFMessage):
 
     def __init__(self, length=None, router_id='0.0.0.0', area_id='0.0.0.0',
                  au_type=1, authentication=0, checksum=None, version=_VERSION,
-                 lsa_requests=[]):
+                 lsa_requests=None):
+        lsa_requests = lsa_requests if lsa_requests else []
         super(OSPFLSReq, self).__init__(OSPF_MSG_LS_REQ, length, router_id,
                                         area_id, au_type, authentication,
                                         checksum, version)
@@ -894,7 +901,8 @@ class OSPFLSUpd(OSPFMessage):
 
     def __init__(self, length=None, router_id='0.0.0.0', area_id='0.0.0.0',
                  au_type=1, authentication=0, checksum=None, version=_VERSION,
-                 lsas=[]):
+                 lsas=None):
+        lsas = lsas if lsas else []
         super(OSPFLSUpd, self).__init__(OSPF_MSG_LS_UPD, length, router_id,
                                         area_id, au_type, authentication,
                                         checksum, version)
@@ -930,7 +938,8 @@ class OSPFLSAck(OSPFMessage):
 
     def __init__(self, length=None, router_id='0.0.0.0', area_id='0.0.0.0',
                  au_type=1, authentication=0, checksum=None, version=_VERSION,
-                 lsa_headers=[]):
+                 lsa_headers=None):
+        lsa_headers = lsa_headers if lsa_headers else []
         super(OSPFLSAck, self).__init__(OSPF_MSG_LS_ACK, length, router_id,
                                         area_id, au_type, authentication,
                                         checksum, version)
diff --git a/ryu/ofproto/ofproto_v1_2_parser.py b/ryu/ofproto/ofproto_v1_2_parser.py
index 7f38e36e..9292b78d 100644
--- a/ryu/ofproto/ofproto_v1_2_parser.py
+++ b/ryu/ofproto/ofproto_v1_2_parser.py
@@ -931,7 +931,8 @@ class OFPFlowMod(MsgBase):
                  buffer_id=ofproto.OFP_NO_BUFFER,
                  out_port=0, out_group=0, flags=0,
                  match=None,
-                 instructions=[]):
+                 instructions=None):
+        instructions = instructions if instructions else []
         super(OFPFlowMod, self).__init__(datapath)
         self.cookie = cookie
         self.cookie_mask = cookie_mask
@@ -1725,7 +1726,8 @@ class OFPGroupMod(MsgBase):
             datapath.send_msg(req)
     """
     def __init__(self, datapath, command=ofproto.OFPGC_ADD,
-                 type_=ofproto.OFPGT_ALL, group_id=0, buckets=[]):
+                 type_=ofproto.OFPGT_ALL, group_id=0, buckets=None):
+        buckets = buckets if buckets else []
         super(OFPGroupMod, self).__init__(datapath)
         self.command = command
         self.type = type_
diff --git a/ryu/ofproto/ofproto_v1_3_parser.py b/ryu/ofproto/ofproto_v1_3_parser.py
index 8d855256..f3e2b45d 100644
--- a/ryu/ofproto/ofproto_v1_3_parser.py
+++ b/ryu/ofproto/ofproto_v1_3_parser.py
@@ -99,7 +99,8 @@ class OFPHello(MsgBase):
     elements   list of ``OFPHelloElemVersionBitmap`` instance
     ========== =========================================================
     """
-    def __init__(self, datapath, elements=[]):
+    def __init__(self, datapath, elements=None):
+        elements = elements if elements else []
         super(OFPHello, self).__init__(datapath)
         self.elements = elements
 
@@ -2607,7 +2608,8 @@ class OFPFlowMod(MsgBase):
                  buffer_id=ofproto.OFP_NO_BUFFER,
                  out_port=0, out_group=0, flags=0,
                  match=None,
-                 instructions=[]):
+                 instructions=None):
+        instructions = instructions if instructions else []
         super(OFPFlowMod, self).__init__(datapath)
         self.cookie = cookie
         self.cookie_mask = cookie_mask
@@ -3504,7 +3506,8 @@ class OFPGroupMod(MsgBase):
             datapath.send_msg(req)
     """
     def __init__(self, datapath, command=ofproto.OFPGC_ADD,
-                 type_=ofproto.OFPGT_ALL, group_id=0, buckets=[]):
+                 type_=ofproto.OFPGT_ALL, group_id=0, buckets=None):
+        buckets = buckets if buckets else []
         super(OFPGroupMod, self).__init__(datapath)
         self.command = command
         self.type = type_
@@ -3635,7 +3638,8 @@ class OFPMeterMod(MsgBase):
     ================ ======================================================
     """
     def __init__(self, datapath, command=ofproto.OFPMC_ADD,
-                 flags=ofproto.OFPMF_KBPS, meter_id=1, bands=[]):
+                 flags=ofproto.OFPMF_KBPS, meter_id=1, bands=None):
+        bands = bands if bands else []
         super(OFPMeterMod, self).__init__(datapath)
         self.command = command
         self.flags = flags
@@ -5133,7 +5137,8 @@ class OFPInstructionId(StringifyMixin):
 @OFPTableFeatureProp.register_type(ofproto.OFPTFPT_INSTRUCTIONS)
 @OFPTableFeatureProp.register_type(ofproto.OFPTFPT_INSTRUCTIONS_MISS)
 class OFPTableFeaturePropInstructions(OFPTableFeatureProp):
-    def __init__(self, type_=None, length=None, instruction_ids=[]):
+    def __init__(self, type_=None, length=None, instruction_ids=None):
+        instruction_ids = instruction_ids if instruction_ids else []
         super(OFPTableFeaturePropInstructions, self).__init__(type_, length)
         self.instruction_ids = instruction_ids
 
@@ -5159,7 +5164,8 @@ class OFPTableFeaturePropInstructions(OFPTableFeatureProp):
 class OFPTableFeaturePropNextTables(OFPTableFeatureProp):
     _TABLE_ID_PACK_STR = '!B'
 
-    def __init__(self, type_=None, length=None, table_ids=[]):
+    def __init__(self, type_=None, length=None, table_ids=None):
+        table_ids = table_ids if table_ids else []
         super(OFPTableFeaturePropNextTables, self).__init__(type_, length)
         self.table_ids = table_ids
 
@@ -5219,7 +5225,8 @@ class OFPActionId(StringifyMixin):
 @OFPTableFeatureProp.register_type(ofproto.OFPTFPT_APPLY_ACTIONS)
 @OFPTableFeatureProp.register_type(ofproto.OFPTFPT_APPLY_ACTIONS_MISS)
 class OFPTableFeaturePropActions(OFPTableFeatureProp):
-    def __init__(self, type_=None, length=None, action_ids=[]):
+    def __init__(self, type_=None, length=None, action_ids=None):
+        action_ids = action_ids if action_ids else []
         super(OFPTableFeaturePropActions, self).__init__(type_, length)
         self.action_ids = action_ids
 
@@ -5327,7 +5334,8 @@ class OFPExperimenterOxmId(OFPOxmId):
 @OFPTableFeatureProp.register_type(ofproto.OFPTFPT_APPLY_SETFIELD)
 @OFPTableFeatureProp.register_type(ofproto.OFPTFPT_APPLY_SETFIELD_MISS)
 class OFPTableFeaturePropOxm(OFPTableFeatureProp):
-    def __init__(self, type_=None, length=None, oxm_ids=[]):
+    def __init__(self, type_=None, length=None, oxm_ids=None):
+        oxm_ids = oxm_ids if oxm_ids else []
         super(OFPTableFeaturePropOxm, self).__init__(type_, length)
         self.oxm_ids = oxm_ids
 
@@ -5369,8 +5377,9 @@ class OFPTableFeaturesStatsRequest(OFPMultipartRequest):
     ================ ======================================================
     """
     def __init__(self, datapath, flags=0,
-                 body=[],
+                 body=None,
                  type_=None):
+        body = body if body else []
         super(OFPTableFeaturesStatsRequest, self).__init__(datapath, flags)
         self.body = body
 
@@ -5586,8 +5595,9 @@ class ONFFlowMonitorStatsRequest(OFPExperimenterStatsRequestBase):
     body             List of ONFFlowMonitorRequest instances
     ================ ======================================================
     """
-    def __init__(self, datapath, flags, body=[],
+    def __init__(self, datapath, flags, body=None,
                  type_=None, experimenter=None, exp_type=None):
+        body = body if body else []
         super(ONFFlowMonitorStatsRequest,
               self).__init__(datapath, flags,
                              experimenter=ofproto_common.ONF_EXPERIMENTER_ID,
diff --git a/ryu/ofproto/ofproto_v1_4_parser.py b/ryu/ofproto/ofproto_v1_4_parser.py
index 86d45683..51e86196 100644
--- a/ryu/ofproto/ofproto_v1_4_parser.py
+++ b/ryu/ofproto/ofproto_v1_4_parser.py
@@ -71,7 +71,8 @@ class OFPHello(MsgBase):
     elements   list of ``OFPHelloElemVersionBitmap`` instance
     ========== =========================================================
     """
-    def __init__(self, datapath, elements=[]):
+    def __init__(self, datapath, elements=None):
+        elements = elements if elements else []
         super(OFPHello, self).__init__(datapath)
         self.elements = elements
 
@@ -1466,7 +1467,8 @@ class OFPMeterMod(MsgBase):
     ================ ======================================================
     """
     def __init__(self, datapath, command=ofproto.OFPMC_ADD,
-                 flags=ofproto.OFPMF_KBPS, meter_id=1, bands=[]):
+                 flags=ofproto.OFPMF_KBPS, meter_id=1, bands=None):
+        bands = bands if bands else []
         super(OFPMeterMod, self).__init__(datapath)
         self.command = command
         self.flags = flags
@@ -1786,7 +1788,8 @@ class OFPInstructionId(StringifyMixin):
 @OFPTableFeatureProp.register_type(ofproto.OFPTFPT_INSTRUCTIONS)
 @OFPTableFeatureProp.register_type(ofproto.OFPTFPT_INSTRUCTIONS_MISS)
 class OFPTableFeaturePropInstructions(OFPTableFeatureProp):
-    def __init__(self, type_=None, length=None, instruction_ids=[]):
+    def __init__(self, type_=None, length=None, instruction_ids=None):
+        instruction_ids = instruction_ids if instruction_ids else []
         super(OFPTableFeaturePropInstructions, self).__init__(type_, length)
         self.instruction_ids = instruction_ids
 
@@ -1838,7 +1841,8 @@ class OFPActionId(StringifyMixin):
 @OFPTableFeatureProp.register_type(ofproto.OFPTFPT_APPLY_ACTIONS)
 @OFPTableFeatureProp.register_type(ofproto.OFPTFPT_APPLY_ACTIONS_MISS)
 class OFPTableFeaturePropActions(OFPTableFeatureProp):
-    def __init__(self, type_=None, length=None, action_ids=[]):
+    def __init__(self, type_=None, length=None, action_ids=None):
+        action_ids = action_ids if action_ids else []
         super(OFPTableFeaturePropActions, self).__init__(type_, length)
         self.action_ids = action_ids
 
@@ -1864,7 +1868,8 @@ class OFPTableFeaturePropActions(OFPTableFeatureProp):
 class OFPTableFeaturePropNextTables(OFPTableFeatureProp):
     _TABLE_ID_PACK_STR = '!B'
 
-    def __init__(self, type_=None, length=None, table_ids=[]):
+    def __init__(self, type_=None, length=None, table_ids=None):
+        table_ids = table_ids if table_ids else []
         super(OFPTableFeaturePropNextTables, self).__init__(type_, length)
         self.table_ids = table_ids
 
@@ -1975,7 +1980,8 @@ class OFPExperimenterOxmId(OFPOxmId):
 @OFPTableFeatureProp.register_type(ofproto.OFPTFPT_APPLY_SETFIELD)
 @OFPTableFeatureProp.register_type(ofproto.OFPTFPT_APPLY_SETFIELD_MISS)
 class OFPTableFeaturePropOxm(OFPTableFeatureProp):
-    def __init__(self, type_=None, length=None, oxm_ids=[]):
+    def __init__(self, type_=None, length=None, oxm_ids=None):
+        oxm_ids = oxm_ids if oxm_ids else []
         super(OFPTableFeaturePropOxm, self).__init__(type_, length)
         self.oxm_ids = oxm_ids
 
@@ -2016,7 +2022,8 @@ class OFPTableFeaturesStatsRequest(OFPMultipartRequest):
                      The default is [].
     ================ ======================================================
     """
-    def __init__(self, datapath, flags=0, body=[], type_=None):
+    def __init__(self, datapath, flags=0, body=None, type_=None):
+        body = body if body else []
         super(OFPTableFeaturesStatsRequest, self).__init__(datapath, flags)
         self.body = body
 
@@ -3055,7 +3062,8 @@ class OFPFlowUpdateHeader(OFPFlowUpdate):
 class OFPFlowUpdateFull(OFPFlowUpdateHeader):
     def __init__(self, length=None, event=None, table_id=None, reason=None,
                  idle_timeout=None, hard_timeout=None, priority=None,
-                 cookie=None, match=None, instructions=[]):
+                 cookie=None, match=None, instructions=None):
+        instructions = instructions if instructions else []
         super(OFPFlowUpdateFull, self).__init__(length, event)
         self.table_id = table_id
         self.reason = reason
@@ -4266,7 +4274,8 @@ class OFPFlowMod(MsgBase):
                  buffer_id=ofproto.OFP_NO_BUFFER,
                  out_port=0, out_group=0, flags=0, importance=0,
                  match=None,
-                 instructions=[]):
+                 instructions=None):
+        instructions = instructions if instructions else []
         super(OFPFlowMod, self).__init__(datapath)
         self.cookie = cookie
         self.cookie_mask = cookie_mask
@@ -5036,7 +5045,8 @@ class OFPGroupMod(MsgBase):
             datapath.send_msg(req)
     """
     def __init__(self, datapath, command=ofproto.OFPGC_ADD,
-                 type_=ofproto.OFPGT_ALL, group_id=0, buckets=[]):
+                 type_=ofproto.OFPGT_ALL, group_id=0, buckets=None):
+        buckets = buckets if buckets else []
         super(OFPGroupMod, self).__init__(datapath)
         self.command = command
         self.type = type_
diff --git a/ryu/ofproto/ofproto_v1_5_parser.py b/ryu/ofproto/ofproto_v1_5_parser.py
index 2d671b72..a6e5136f 100644
--- a/ryu/ofproto/ofproto_v1_5_parser.py
+++ b/ryu/ofproto/ofproto_v1_5_parser.py
@@ -73,7 +73,8 @@ class OFPHello(MsgBase):
     elements   list of ``OFPHelloElemVersionBitmap`` instance
     ========== =========================================================
     """
-    def __init__(self, datapath, elements=[]):
+    def __init__(self, datapath, elements=None):
+        elements = elements if elements else []
         super(OFPHello, self).__init__(datapath)
         self.elements = elements
 
@@ -1135,7 +1136,8 @@ class OFPPortDescPropOptical(OFPPortDescProp):
 @OFPPortDescProp.register_type(ofproto.OFPPDPT_PIPELINE_INPUT)
 @OFPPortDescProp.register_type(ofproto.OFPPDPT_PIPELINE_OUTPUT)
 class OFPPortDescPropOxm(OFPPortDescProp):
-    def __init__(self, type_=None, length=None, oxm_ids=[]):
+    def __init__(self, type_=None, length=None, oxm_ids=None):
+        oxm_ids = oxm_ids if oxm_ids else []
         super(OFPPortDescPropOxm, self).__init__(type_, length)
         self.oxm_ids = oxm_ids
 
@@ -1159,7 +1161,8 @@ class OFPPortDescPropOxm(OFPPortDescProp):
 class OFPPortDescPropRecirculate(OFPPortDescProp):
     _PORT_NO_PACK_STR = '!I'
 
-    def __init__(self, type_=None, length=None, port_nos=[]):
+    def __init__(self, type_=None, length=None, port_nos=None):
+        port_nos = port_nos if port_nos else []
         super(OFPPortDescPropRecirculate, self).__init__(type_, length)
         self.port_nos = port_nos
 
@@ -1702,7 +1705,8 @@ class OFPMeterMod(MsgBase):
     ================ ======================================================
     """
     def __init__(self, datapath, command=ofproto.OFPMC_ADD,
-                 flags=ofproto.OFPMF_KBPS, meter_id=1, bands=[]):
+                 flags=ofproto.OFPMF_KBPS, meter_id=1, bands=None):
+        bands = bands if bands else []
         super(OFPMeterMod, self).__init__(datapath)
         self.command = command
         self.flags = flags
@@ -2023,7 +2027,8 @@ class OFPInstructionId(StringifyMixin):
 @OFPTableFeatureProp.register_type(ofproto.OFPTFPT_INSTRUCTIONS)
 @OFPTableFeatureProp.register_type(ofproto.OFPTFPT_INSTRUCTIONS_MISS)
 class OFPTableFeaturePropInstructions(OFPTableFeatureProp):
-    def __init__(self, type_=None, length=None, instruction_ids=[]):
+    def __init__(self, type_=None, length=None, instruction_ids=None):
+        instruction_ids = instruction_ids if instruction_ids else []
         super(OFPTableFeaturePropInstructions, self).__init__(type_, length)
         self.instruction_ids = instruction_ids
 
@@ -2075,7 +2080,8 @@ class OFPActionId(StringifyMixin):
 @OFPTableFeatureProp.register_type(ofproto.OFPTFPT_APPLY_ACTIONS)
 @OFPTableFeatureProp.register_type(ofproto.OFPTFPT_APPLY_ACTIONS_MISS)
 class OFPTableFeaturePropActions(OFPTableFeatureProp):
-    def __init__(self, type_=None, length=None, action_ids=[]):
+    def __init__(self, type_=None, length=None, action_ids=None):
+        action_ids = action_ids if action_ids else []
         super(OFPTableFeaturePropActions, self).__init__(type_, length)
         self.action_ids = action_ids
 
@@ -2101,7 +2107,8 @@ class OFPTableFeaturePropActions(OFPTableFeatureProp):
 class OFPTableFeaturePropNextTables(OFPTableFeatureProp):
     _TABLE_ID_PACK_STR = '!B'
 
-    def __init__(self, type_=None, length=None, table_ids=[]):
+    def __init__(self, type_=None, length=None, table_ids=None):
+        table_ids = table_ids if table_ids else []
         super(OFPTableFeaturePropNextTables, self).__init__(type_, length)
         self.table_ids = table_ids
 
@@ -2216,7 +2223,8 @@ class OFPExperimenterOxmId(OFPOxmId):
 @OFPTableFeatureProp.register_type(ofproto.OFPTFPT_APPLY_COPYFIELD)
 @OFPTableFeatureProp.register_type(ofproto.OFPTFPT_APPLY_COPYFIELD_MISS)
 class OFPTableFeaturePropOxm(OFPTableFeatureProp):
-    def __init__(self, type_=None, length=None, oxm_ids=[]):
+    def __init__(self, type_=None, length=None, oxm_ids=None):
+        oxm_ids = oxm_ids if oxm_ids else []
         super(OFPTableFeaturePropOxm, self).__init__(type_, length)
         self.oxm_ids = oxm_ids
 
@@ -2338,7 +2346,8 @@ class OFPTableFeaturesStatsRequest(OFPMultipartRequest):
                      The default is [].
     ================ ======================================================
     """
-    def __init__(self, datapath, flags=0, body=[], type_=None):
+    def __init__(self, datapath, flags=0, body=None, type_=None):
+        body = body if body else []
         super(OFPTableFeaturesStatsRequest, self).__init__(datapath, flags)
         self.body = body
 
@@ -2789,8 +2798,10 @@ class OFPGroupStatsReply(OFPMultipartReply):
 
 
 class OFPGroupDescStats(StringifyMixin):
-    def __init__(self, type_=None, group_id=None, buckets=[], properties=[],
+    def __init__(self, type_=None, group_id=None, buckets=None, properties=None,
                  length=None, bucket_array_len=None):
+        buckets = buckets if buckets else []
+        properties = properties if properties else []
         super(OFPGroupDescStats, self).__init__()
         self.length = length
         self.type = type_
@@ -3405,7 +3416,8 @@ class OFPFlowUpdateHeader(OFPFlowUpdate):
 class OFPFlowUpdateFull(OFPFlowUpdateHeader):
     def __init__(self, length=None, event=None, table_id=None, reason=None,
                  idle_timeout=None, hard_timeout=None, priority=None,
-                 cookie=None, match=None, instructions=[]):
+                 cookie=None, match=None, instructions=None):
+        instructions = instructions if instructions else []
         super(OFPFlowUpdateFull, self).__init__(length, event)
         self.table_id = table_id
         self.reason = reason
@@ -3716,7 +3728,8 @@ class OFPBundleFeaturesStatsRequest(OFPMultipartRequest):
             datapath.send_msg(req)
     """
     def __init__(self, datapath, flags=0, feature_request_flags=0,
-                 properties=[], type_=None):
+                 properties=None, type_=None):
+        properties = properties if properties else []
         super(OFPBundleFeaturesStatsRequest, self).__init__(datapath, flags)
         self.feature_request_flags = feature_request_flags
         self.properties = properties
@@ -5121,7 +5134,8 @@ class OFPFlowMod(MsgBase):
                  buffer_id=ofproto.OFP_NO_BUFFER,
                  out_port=0, out_group=0, flags=0, importance=0,
                  match=None,
-                 instructions=[]):
+                 instructions=None):
+        instructions = instructions if instructions else []
         super(OFPFlowMod, self).__init__(datapath)
         self.cookie = cookie
         self.cookie_mask = cookie_mask
@@ -5842,8 +5856,9 @@ class OFPActionCopyField(OFPAction):
                      The default is [].
     ================ ======================================================
     """
-    def __init__(self, n_bits=0, src_offset=0, dst_offset=0, oxm_ids=[],
+    def __init__(self, n_bits=0, src_offset=0, dst_offset=0, oxm_ids=None,
                  type_=None, len_=None):
+        oxm_ids = oxm_ids if oxm_ids else []
         super(OFPActionCopyField, self).__init__()
         self.n_bits = n_bits
         self.src_offset = src_offset
@@ -6029,7 +6044,9 @@ class OFPGroupMod(MsgBase):
     """
     def __init__(self, datapath, command=ofproto.OFPGC_ADD,
                  type_=ofproto.OFPGT_ALL, group_id=0, command_bucket_id=0,
-                 buckets=[], properties=[], bucket_array_len=None):
+                 buckets=None, properties=None, bucket_array_len=None):
+        buckets = buckets if buckets else []
+        properties = properties if properties else []
         super(OFPGroupMod, self).__init__(datapath)
         self.command = command
         self.type = type_
@@ -6258,8 +6275,10 @@ class OFPGroupBucketPropExperimenter(OFPPropCommonExperimenter4ByteData):
 
 
 class OFPBucket(StringifyMixin):
-    def __init__(self, bucket_id=0, actions=[], properties=[],
+    def __init__(self, bucket_id=0, actions=None, properties=None,
                  len_=None, action_array_len=None):
+        actions = actions if actions else []
+        properties = properties if properties else []
         super(OFPBucket, self).__init__()
         self.bucket_id = bucket_id
         self.actions = actions
diff --git a/ryu/services/protocols/bgp/api/operator.py b/ryu/services/protocols/bgp/api/operator.py
index acaa5c79..5109b007 100644
--- a/ryu/services/protocols/bgp/api/operator.py
+++ b/ryu/services/protocols/bgp/api/operator.py
@@ -65,7 +65,8 @@ class OperatorApi(object):
     def clear(self, **kwargs):
         return self._run('clear', kw=kwargs)
 
-    def _run(self, cmd, kw={}):
+    def _run(self, cmd, kw=None):
+        kw = kw if kw else {}
         params = kw.get('params', [])
         fmt = kw.get('format', 'json')
         root = RootCmd(api=self.internal_api, resp_formatter_name=fmt)
diff --git a/ryu/utils.py b/ryu/utils.py
index e915e0d9..a8eb5094 100644
--- a/ryu/utils.py
+++ b/ryu/utils.py
@@ -125,8 +125,9 @@ def get_reqs_from_files(requirements_files):
     return []
 
 
-def parse_requirements(requirements_files=['requirements.txt',
-                                           'tools/pip-requires']):
+def parse_requirements(requirements_files=None):
+    requirements_files = requirements_files if requirements_files else [
+        'requirements.txt', 'tools/pip-requires']
     requirements = []
     for line in get_reqs_from_files(requirements_files):
         # For the requirements list, we need to inject only the portion