diff --git a/hbmqtt/client.py b/hbmqtt/client.py
index b213ef5..253a5a0 100644
--- a/hbmqtt/client.py
+++ b/hbmqtt/client.py
@@ -2,6 +2,7 @@
 #
 # See the file license.txt for copying permission.
 
+import asyncio
 import logging
 import ssl
 from urllib.parse import urlparse, urlunparse
@@ -9,13 +10,12 @@ from functools import wraps
 
 from hbmqtt.utils import not_in_dict_or_none
 from hbmqtt.session import Session
-from hbmqtt.mqtt.connack import *
-from hbmqtt.mqtt.connect import *
+from hbmqtt.mqtt.connack import CONNECTION_ACCEPTED
 from hbmqtt.mqtt.protocol.client_handler import ClientProtocolHandler
 from hbmqtt.adapters import StreamReaderAdapter, StreamWriterAdapter, WebSocketsReader, WebSocketsWriter
 from hbmqtt.plugins.manager import PluginManager, BaseContext
 from hbmqtt.mqtt.protocol.handler import ProtocolHandlerException
-from hbmqtt.mqtt.constants import *
+from hbmqtt.mqtt.constants import QOS_0, QOS_1, QOS_2
 import websockets
 from websockets.uri import InvalidURI
 from websockets.handshake import InvalidHandshake
diff --git a/hbmqtt/mqtt/__init__.py b/hbmqtt/mqtt/__init__.py
index 52fc81d..8c80c38 100644
--- a/hbmqtt/mqtt/__init__.py
+++ b/hbmqtt/mqtt/__init__.py
@@ -2,7 +2,10 @@
 #
 # See the file license.txt for copying permission.
 from hbmqtt.errors import HBMQTTException
-from hbmqtt.mqtt.packet import *
+from hbmqtt.mqtt.packet import (
+    CONNECT, CONNACK, PUBLISH, PUBACK, PUBREC, PUBREL, PUBCOMP, SUBSCRIBE,
+    SUBACK, UNSUBSCRIBE, UNSUBACK, PINGREQ, PINGRESP, DISCONNECT,
+    MQTTFixedHeader)
 from hbmqtt.mqtt.connect import ConnectPacket
 from hbmqtt.mqtt.connack import ConnackPacket
 from hbmqtt.mqtt.disconnect import DisconnectPacket
diff --git a/hbmqtt/mqtt/connect.py b/hbmqtt/mqtt/connect.py
index 79d6b39..c82a45b 100644
--- a/hbmqtt/mqtt/connect.py
+++ b/hbmqtt/mqtt/connect.py
@@ -1,8 +1,10 @@
 # Copyright (c) 2015 Nicolas JOUANIN
 #
 # See the file license.txt for copying permission.
+import asyncio
+
+from hbmqtt.codecs import bytes_to_int, decode_data_with_length, decode_string, encode_data_with_length, encode_string, int_to_bytes, read_or_raise
 from hbmqtt.mqtt.packet import MQTTPacket, MQTTFixedHeader, CONNECT, MQTTVariableHeader, MQTTPayload
-from hbmqtt.codecs import *
 from hbmqtt.errors import HBMQTTException, NoDataException
 from hbmqtt.adapters import ReaderAdapter
 
diff --git a/hbmqtt/mqtt/packet.py b/hbmqtt/mqtt/packet.py
index a799e78..3d682a6 100644
--- a/hbmqtt/mqtt/packet.py
+++ b/hbmqtt/mqtt/packet.py
@@ -1,8 +1,10 @@
 # Copyright (c) 2015 Nicolas JOUANIN
 #
 # See the file license.txt for copying permission.
-from hbmqtt.errors import CodecException, MQTTException
-from hbmqtt.codecs import *
+import asyncio
+
+from hbmqtt.codecs import bytes_to_hex_str, decode_packet_id, int_to_bytes, read_or_raise
+from hbmqtt.errors import CodecException, MQTTException, NoDataException
 from hbmqtt.adapters import ReaderAdapter, WriterAdapter
 from datetime import datetime
 from struct import unpack
diff --git a/hbmqtt/mqtt/protocol/broker_handler.py b/hbmqtt/mqtt/protocol/broker_handler.py
index 09509c2..6acf470 100644
--- a/hbmqtt/mqtt/protocol/broker_handler.py
+++ b/hbmqtt/mqtt/protocol/broker_handler.py
@@ -4,8 +4,10 @@
 import asyncio
 from asyncio import futures, Queue
 from hbmqtt.mqtt.protocol.handler import ProtocolHandler
+from hbmqtt.mqtt.connack import (
+    CONNECTION_ACCEPTED, UNACCEPTABLE_PROTOCOL_VERSION, IDENTIFIER_REJECTED,
+    BAD_USERNAME_PASSWORD, NOT_AUTHORIZED, ConnackPacket)
 from hbmqtt.mqtt.connect import ConnectPacket
-from hbmqtt.mqtt.connack import *
 from hbmqtt.mqtt.pingreq import PingReqPacket
 from hbmqtt.mqtt.pingresp import PingRespPacket
 from hbmqtt.mqtt.subscribe import SubscribePacket
diff --git a/hbmqtt/mqtt/protocol/handler.py b/hbmqtt/mqtt/protocol/handler.py
index 744b91e..d1e8b24 100644
--- a/hbmqtt/mqtt/protocol/handler.py
+++ b/hbmqtt/mqtt/protocol/handler.py
@@ -5,12 +5,16 @@ import logging
 import collections
 import itertools
 
+import asyncio
 from asyncio import InvalidStateError
 
 from hbmqtt.mqtt import packet_class
-from hbmqtt.mqtt.packet import *
 from hbmqtt.mqtt.connack import ConnackPacket
 from hbmqtt.mqtt.connect import ConnectPacket
+from hbmqtt.mqtt.packet import (
+    RESERVED_0, CONNECT, CONNACK, PUBLISH, PUBACK, PUBREC, PUBREL, PUBCOMP,
+    SUBSCRIBE, SUBACK, UNSUBSCRIBE, UNSUBACK, PINGREQ, PINGRESP, DISCONNECT,
+    RESERVED_15, MQTTFixedHeader)
 from hbmqtt.mqtt.pingresp import PingRespPacket
 from hbmqtt.mqtt.pingreq import PingReqPacket
 from hbmqtt.mqtt.publish import PublishPacket
@@ -25,9 +29,9 @@ from hbmqtt.mqtt.unsuback import UnsubackPacket
 from hbmqtt.mqtt.disconnect import DisconnectPacket
 from hbmqtt.adapters import ReaderAdapter, WriterAdapter
 from hbmqtt.session import Session, OutgoingApplicationMessage, IncomingApplicationMessage, INCOMING, OUTGOING
-from hbmqtt.mqtt.constants import *
+from hbmqtt.mqtt.constants import QOS_0, QOS_1, QOS_2
 from hbmqtt.plugins.manager import PluginManager
-from hbmqtt.errors import HBMQTTException
+from hbmqtt.errors import HBMQTTException, MQTTException, NoDataException
 
 import sys
 if sys.version_info < (3, 5):
diff --git a/hbmqtt/mqtt/publish.py b/hbmqtt/mqtt/publish.py
index ce52ba1..a33c6fd 100644
--- a/hbmqtt/mqtt/publish.py
+++ b/hbmqtt/mqtt/publish.py
@@ -1,9 +1,11 @@
 # Copyright (c) 2015 Nicolas JOUANIN
 #
 # See the file license.txt for copying permission.
+import asyncio
+
 from hbmqtt.mqtt.packet import MQTTPacket, MQTTFixedHeader, PUBLISH, MQTTVariableHeader, MQTTPayload
 from hbmqtt.errors import HBMQTTException, MQTTException
-from hbmqtt.codecs import *
+from hbmqtt.codecs import decode_packet_id, decode_string, encode_string, int_to_bytes
 
 
 class PublishVariableHeader(MQTTVariableHeader):
diff --git a/hbmqtt/mqtt/suback.py b/hbmqtt/mqtt/suback.py
index f965764..b5966b2 100644
--- a/hbmqtt/mqtt/suback.py
+++ b/hbmqtt/mqtt/suback.py
@@ -1,10 +1,12 @@
 # Copyright (c) 2015 Nicolas JOUANIN
 #
 # See the file license.txt for copying permission.
+import asyncio
+
 from hbmqtt.mqtt.packet import MQTTPacket, MQTTFixedHeader, SUBACK, PacketIdVariableHeader, MQTTPayload, MQTTVariableHeader
-from hbmqtt.errors import HBMQTTException
+from hbmqtt.errors import HBMQTTException, NoDataException
 from hbmqtt.adapters import ReaderAdapter
-from hbmqtt.codecs import *
+from hbmqtt.codecs import bytes_to_int, int_to_bytes, read_or_raise
 
 
 class SubackPayload(MQTTPayload):
diff --git a/hbmqtt/mqtt/subscribe.py b/hbmqtt/mqtt/subscribe.py
index 0a2a9b2..c814b34 100644
--- a/hbmqtt/mqtt/subscribe.py
+++ b/hbmqtt/mqtt/subscribe.py
@@ -1,9 +1,11 @@
 # Copyright (c) 2015 Nicolas JOUANIN
 #
 # See the file license.txt for copying permission.
+import asyncio
+
 from hbmqtt.mqtt.packet import MQTTPacket, MQTTFixedHeader, SUBSCRIBE, PacketIdVariableHeader, MQTTPayload, MQTTVariableHeader
-from hbmqtt.errors import HBMQTTException
-from hbmqtt.codecs import *
+from hbmqtt.errors import HBMQTTException, NoDataException
+from hbmqtt.codecs import bytes_to_int, decode_string, encode_string, int_to_bytes, read_or_raise
 
 
 class SubscribePayload(MQTTPayload):
diff --git a/hbmqtt/mqtt/unsubscribe.py b/hbmqtt/mqtt/unsubscribe.py
index b12f460..cb7839a 100644
--- a/hbmqtt/mqtt/unsubscribe.py
+++ b/hbmqtt/mqtt/unsubscribe.py
@@ -1,9 +1,11 @@
 # Copyright (c) 2015 Nicolas JOUANIN
 #
 # See the file license.txt for copying permission.
+import asyncio
+
 from hbmqtt.mqtt.packet import MQTTPacket, MQTTFixedHeader, UNSUBSCRIBE, PacketIdVariableHeader, MQTTPayload, MQTTVariableHeader
-from hbmqtt.errors import HBMQTTException
-from hbmqtt.codecs import *
+from hbmqtt.errors import HBMQTTException, NoDataException
+from hbmqtt.codecs import decode_string, encode_string
 
 
 class UnubscribePayload(MQTTPayload):
diff --git a/hbmqtt/utils.py b/hbmqtt/utils.py
index 1c2a104..8eca44a 100644
--- a/hbmqtt/utils.py
+++ b/hbmqtt/utils.py
@@ -1,9 +1,14 @@
 # Copyright (c) 2015 Nicolas JOUANIN
 #
 # See the file license.txt for copying permission.
+import logging
+
 import yaml
 
 
+logger = logging.getLogger(__name__)
+
+
 def not_in_dict_or_none(dict, key):
     """
     Check if a key exists in a map and if it's not None
diff --git a/samples/client_publish.py b/samples/client_publish.py
index 6e150ad..fc9d0e0 100644
--- a/samples/client_publish.py
+++ b/samples/client_publish.py
@@ -2,7 +2,7 @@ import logging
 import asyncio
 
 from hbmqtt.client import MQTTClient, ConnectException
-from hbmqtt.mqtt.constants import *
+from hbmqtt.mqtt.constants import QOS_1, QOS_2
 
 
 #
diff --git a/tests/mqtt/protocol/test_handler.py b/tests/mqtt/protocol/test_handler.py
index d890bcd..5a8180e 100644
--- a/tests/mqtt/protocol/test_handler.py
+++ b/tests/mqtt/protocol/test_handler.py
@@ -9,7 +9,7 @@ from hbmqtt.plugins.manager import PluginManager
 from hbmqtt.session import Session, OutgoingApplicationMessage, IncomingApplicationMessage
 from hbmqtt.mqtt.protocol.handler import ProtocolHandler
 from hbmqtt.adapters import StreamWriterAdapter, StreamReaderAdapter
-from hbmqtt.mqtt.constants import *
+from hbmqtt.mqtt.constants import QOS_0, QOS_1, QOS_2
 from hbmqtt.mqtt.publish import PublishPacket
 from hbmqtt.mqtt.puback import PubackPacket
 from hbmqtt.mqtt.pubrec import PubrecPacket
diff --git a/tests/mqtt/test_puback.py b/tests/mqtt/test_puback.py
index 2a20d99..14f6691 100644
--- a/tests/mqtt/test_puback.py
+++ b/tests/mqtt/test_puback.py
@@ -1,10 +1,10 @@
 # Copyright (c) 2015 Nicolas JOUANIN
 #
 # See the file license.txt for copying permission.
+import asyncio
 import unittest
 
 from hbmqtt.mqtt.puback import PubackPacket, PacketIdVariableHeader
-from hbmqtt.codecs import *
 from hbmqtt.adapters import BufferReader
 
 
diff --git a/tests/mqtt/test_pubcomp.py b/tests/mqtt/test_pubcomp.py
index 25c0a2c..540fc41 100644
--- a/tests/mqtt/test_pubcomp.py
+++ b/tests/mqtt/test_pubcomp.py
@@ -1,11 +1,11 @@
 # Copyright (c) 2015 Nicolas JOUANIN
 #
 # See the file license.txt for copying permission.
+import asyncio
 import unittest
 
 from hbmqtt.mqtt.pubcomp import PubcompPacket, PacketIdVariableHeader
 from hbmqtt.adapters import BufferReader
-from hbmqtt.codecs import *
 
 
 class PubcompPacketTest(unittest.TestCase):
diff --git a/tests/mqtt/test_publish.py b/tests/mqtt/test_publish.py
index ac34a0b..06c2913 100644
--- a/tests/mqtt/test_publish.py
+++ b/tests/mqtt/test_publish.py
@@ -1,11 +1,11 @@
 # Copyright (c) 2015 Nicolas JOUANIN
 #
 # See the file license.txt for copying permission.
+import asyncio
 import unittest
 
 from hbmqtt.mqtt.publish import PublishPacket, PublishVariableHeader, PublishPayload
 from hbmqtt.adapters import BufferReader
-from hbmqtt.codecs import *
 from hbmqtt.mqtt.constants import QOS_0, QOS_1, QOS_2
 
 
diff --git a/tests/mqtt/test_pubrec.py b/tests/mqtt/test_pubrec.py
index e1092df..b376b72 100644
--- a/tests/mqtt/test_pubrec.py
+++ b/tests/mqtt/test_pubrec.py
@@ -1,11 +1,11 @@
 # Copyright (c) 2015 Nicolas JOUANIN
 #
 # See the file license.txt for copying permission.
+import asyncio
 import unittest
 
 from hbmqtt.mqtt.pubrec import PubrecPacket, PacketIdVariableHeader
 from hbmqtt.adapters import BufferReader
-from hbmqtt.codecs import *
 
 
 class PubrecPacketTest(unittest.TestCase):
diff --git a/tests/mqtt/test_pubrel.py b/tests/mqtt/test_pubrel.py
index 516f9d8..385d0e3 100644
--- a/tests/mqtt/test_pubrel.py
+++ b/tests/mqtt/test_pubrel.py
@@ -1,10 +1,10 @@
 # Copyright (c) 2015 Nicolas JOUANIN
 #
 # See the file license.txt for copying permission.
+import asyncio
 import unittest
 
 from hbmqtt.mqtt.pubrel import PubrelPacket, PacketIdVariableHeader
-from hbmqtt.codecs import *
 from hbmqtt.adapters import BufferReader
 
 
diff --git a/tests/mqtt/test_suback.py b/tests/mqtt/test_suback.py
index 9e6613d..c0b0e8a 100644
--- a/tests/mqtt/test_suback.py
+++ b/tests/mqtt/test_suback.py
@@ -1,12 +1,12 @@
 # Copyright (c) 2015 Nicolas JOUANIN
 #
 # See the file license.txt for copying permission.
+import asyncio
 import unittest
 
 from hbmqtt.mqtt.suback import SubackPacket, SubackPayload
 from hbmqtt.mqtt.packet import PacketIdVariableHeader
 from hbmqtt.adapters import BufferReader
-from hbmqtt.codecs import *
 
 
 class SubackPacketTest(unittest.TestCase):
diff --git a/tests/mqtt/test_subscribe.py b/tests/mqtt/test_subscribe.py
index 7e58329..18f8f58 100644
--- a/tests/mqtt/test_subscribe.py
+++ b/tests/mqtt/test_subscribe.py
@@ -1,12 +1,12 @@
 # Copyright (c) 2015 Nicolas JOUANIN
 #
 # See the file license.txt for copying permission.
+import asyncio
 import unittest
 
 from hbmqtt.mqtt.subscribe import SubscribePacket, SubscribePayload
 from hbmqtt.mqtt.packet import PacketIdVariableHeader
-from hbmqtt.mqtt.constants import *
-from hbmqtt.codecs import *
+from hbmqtt.mqtt.constants import QOS_1, QOS_2
 from hbmqtt.adapters import BufferReader
 
 
diff --git a/tests/mqtt/test_unsuback.py b/tests/mqtt/test_unsuback.py
index 91650d0..376ba6b 100644
--- a/tests/mqtt/test_unsuback.py
+++ b/tests/mqtt/test_unsuback.py
@@ -1,12 +1,12 @@
 # Copyright (c) 2015 Nicolas JOUANIN
 #
 # See the file license.txt for copying permission.
+import asyncio
 import unittest
 
 from hbmqtt.mqtt.unsuback import UnsubackPacket
 from hbmqtt.mqtt.packet import PacketIdVariableHeader
 from hbmqtt.adapters import BufferReader
-from hbmqtt.codecs import *
 
 
 class UnsubackPacketTest(unittest.TestCase):
diff --git a/tests/mqtt/test_unsubscribe.py b/tests/mqtt/test_unsubscribe.py
index 3c3c750..fc97c02 100644
--- a/tests/mqtt/test_unsubscribe.py
+++ b/tests/mqtt/test_unsubscribe.py
@@ -1,12 +1,12 @@
 # Copyright (c) 2015 Nicolas JOUANIN
 #
 # See the file license.txt for copying permission.
+import asyncio
 import unittest
 
 from hbmqtt.mqtt.unsubscribe import UnsubscribePacket, UnubscribePayload
 from hbmqtt.mqtt.packet import PacketIdVariableHeader
 from hbmqtt.adapters import BufferReader
-from hbmqtt.codecs import *
 
 
 class UnsubscribePacketTest(unittest.TestCase):
diff --git a/tests/test_broker.py b/tests/test_broker.py
index fa031df..835efaf 100644
--- a/tests/test_broker.py
+++ b/tests/test_broker.py
@@ -1,14 +1,35 @@
 # Copyright (c) 2015 Nicolas JOUANIN
 #
 # See the file license.txt for copying permission.
+import asyncio
+import logging
 import unittest
 from unittest.mock import patch, call
-from hbmqtt.broker import *
-from hbmqtt.mqtt.constants import *
+
+from hbmqtt.adapters import StreamReaderAdapter, StreamWriterAdapter
+from hbmqtt.broker import (
+    EVENT_BROKER_PRE_START,
+    EVENT_BROKER_POST_START,
+    EVENT_BROKER_PRE_SHUTDOWN,
+    EVENT_BROKER_POST_SHUTDOWN,
+    EVENT_BROKER_CLIENT_CONNECTED,
+    EVENT_BROKER_CLIENT_DISCONNECTED,
+    EVENT_BROKER_CLIENT_SUBSCRIBED,
+    EVENT_BROKER_CLIENT_UNSUBSCRIBED,
+    EVENT_BROKER_MESSAGE_RECEIVED,
+    Broker)
 from hbmqtt.client import MQTTClient, ConnectException
-from hbmqtt.mqtt import ConnectPacket, ConnackPacket, PublishPacket, PubrecPacket, \
-    PubrelPacket, PubcompPacket, DisconnectPacket
+from hbmqtt.mqtt import (
+    ConnectPacket, ConnackPacket, PublishPacket, PubrecPacket,
+    PubrelPacket, PubcompPacket, DisconnectPacket)
 from hbmqtt.mqtt.connect import ConnectVariableHeader, ConnectPayload
+from hbmqtt.mqtt.constants import QOS_0, QOS_1, QOS_2
+
+import sys
+if sys.version_info < (3, 5):
+    from asyncio import async as ensure_future
+else:
+    from asyncio import ensure_future
 
 formatter = "[%(asctime)s] %(name)s {%(filename)s:%(lineno)d} %(levelname)s - %(message)s"
 logging.basicConfig(level=logging.DEBUG, format=formatter)
diff --git a/tests/test_client.py b/tests/test_client.py
index 905ade8..99f11d5 100644
--- a/tests/test_client.py
+++ b/tests/test_client.py
@@ -7,7 +7,7 @@ import os
 import logging
 from hbmqtt.client import MQTTClient, ConnectException
 from hbmqtt.broker import Broker
-from hbmqtt.mqtt.constants import *
+from hbmqtt.mqtt.constants import QOS_0, QOS_1, QOS_2
 
 formatter = "[%(asctime)s] %(name)s {%(filename)s:%(lineno)d} %(levelname)s - %(message)s"
 logging.basicConfig(level=logging.ERROR, format=formatter)
diff --git a/tox.ini b/tox.ini
index d6c9d0e..66a4332 100644
--- a/tox.ini
+++ b/tox.ini
@@ -1,11 +1,8 @@
 [flake8]
 ignore =
-    F403,  # 'from x import *' used; unable to detect undefined names (~29 warnings)
-    F821,  # undefined name 'x' (~1 warnings)
     F841,  # local variable 'wildcard_pattern' is assigned to but never used (~17 warnings)
     E265,  # block comment should start with '# ' (~64 warnings)
     E501,  # line too long  (~664 warnings)
-    F405,  # 'x' may be undefined, or defined from star imports (~401 warnings)
 
 [tox]
 envlist =