diff --git a/kafka/client_async.py b/kafka/client_async.py
index bd34c3b2d..b72c05dac 100644
--- a/kafka/client_async.py
+++ b/kafka/client_async.py
@@ -19,7 +19,7 @@
 from kafka.vendor import six
 
 from kafka.cluster import ClusterMetadata
-from kafka.conn import BrokerConnection, ConnectionStates, collect_hosts, get_ip_port_afi
+from kafka.conn import BrokerConnection, ConnectionStates, get_ip_port_afi
 from kafka import errors as Errors
 from kafka.future import Future
 from kafka.metrics import AnonMeasurable
diff --git a/kafka/conn.py b/kafka/conn.py
index 857b13a57..7287a4840 100644
--- a/kafka/conn.py
+++ b/kafka/conn.py
@@ -14,7 +14,6 @@
     from kafka.vendor import selectors34 as selectors
 
 import socket
-import struct
 import threading
 import time
 
@@ -23,7 +22,6 @@
 import kafka.errors as Errors
 from kafka.future import Future
 from kafka.metrics.stats import Avg, Count, Max, Rate
-from kafka.oauth.abstract import AbstractTokenProvider
 from kafka.protocol.admin import DescribeAclsRequest, DescribeClientQuotasRequest, ListGroupsRequest
 from kafka.protocol.api_versions import ApiVersionsRequest
 from kafka.protocol.broker_api_versions import BROKER_API_VERSIONS
@@ -36,7 +34,7 @@
 from kafka.protocol.produce import ProduceRequest
 from kafka.protocol.sasl_authenticate import SaslAuthenticateRequest
 from kafka.protocol.sasl_handshake import SaslHandshakeRequest
-from kafka.protocol.types import Int32, Int8
+from kafka.protocol.types import Int32
 from kafka.sasl import get_sasl_mechanism
 from kafka.version import __version__
 
@@ -1151,7 +1149,8 @@ def timed_out_ifrs(self):
     def next_ifr_request_timeout_ms(self):
         with self._lock:
             if self.in_flight_requests:
-                get_timeout = lambda v: v[2]
+                def get_timeout(v):
+                    return v[2]
                 next_timeout = min(map(get_timeout,
                                    self.in_flight_requests.values()))
                 return max(0, (next_timeout - time.time()) * 1000)
@@ -1159,11 +1158,11 @@ def next_ifr_request_timeout_ms(self):
                 return float('inf')
 
     def get_api_versions(self):
-        if self._api_versions is not None:
-            return self._api_versions
-
-        version = self.check_version()
-        # _api_versions is set as a side effect of check_versions()
+        # _api_versions is set as a side effect of first connection
+        # which should typically be bootstrap, but call check_version
+        # if that hasn't happened yet
+        if self._api_versions is None:
+            self.check_version()
         return self._api_versions
 
     def _infer_broker_version_from_api_versions(self, api_versions):
@@ -1201,11 +1200,11 @@ def _infer_broker_version_from_api_versions(self, api_versions):
         ]
 
         # Get the best match of test cases
-        for broker_version, struct in sorted(test_cases, reverse=True):
-            if struct.API_KEY not in api_versions:
+        for broker_version, proto_struct in sorted(test_cases, reverse=True):
+            if proto_struct.API_KEY not in api_versions:
                 continue
-            min_version, max_version = api_versions[struct.API_KEY]
-            if min_version <= struct.API_VERSION <= max_version:
+            min_version, max_version = api_versions[proto_struct.API_KEY]
+            if min_version <= proto_struct.API_VERSION <= max_version:
                 return broker_version
 
         # We know that ApiVersionsResponse is only supported in 0.10+
diff --git a/kafka/consumer/fetcher.py b/kafka/consumer/fetcher.py
index eefac5ba7..a833a5b79 100644
--- a/kafka/consumer/fetcher.py
+++ b/kafka/consumer/fetcher.py
@@ -501,7 +501,7 @@ def _unpack_records(self, tp, records):
         # If unpacking raises StopIteration, it is erroneously
         # caught by the generator. We want all exceptions to be raised
         # back to the user. See Issue 545
-        except StopIteration as e:
+        except StopIteration:
             log.exception('StopIteration raised unpacking messageset')
             raise RuntimeError('StopIteration raised unpacking messageset')
 
@@ -1001,7 +1001,7 @@ def build_next(self, next_partitions):
             log.debug("Built full fetch %s for node %s with %s partition(s).",
                 self.next_metadata, self.node_id, len(next_partitions))
             self.session_partitions = next_partitions
-            return FetchRequestData(next_partitions, None, self.next_metadata);
+            return FetchRequestData(next_partitions, None, self.next_metadata)
 
         prev_tps = set(self.session_partitions.keys())
         next_tps = set(next_partitions.keys())
diff --git a/kafka/coordinator/assignors/sticky/sticky_assignor.py b/kafka/coordinator/assignors/sticky/sticky_assignor.py
index dce714f1a..6e79c597e 100644
--- a/kafka/coordinator/assignors/sticky/sticky_assignor.py
+++ b/kafka/coordinator/assignors/sticky/sticky_assignor.py
@@ -2,7 +2,6 @@
 from collections import defaultdict, namedtuple
 from copy import deepcopy
 
-from kafka.cluster import ClusterMetadata
 from kafka.coordinator.assignors.abstract import AbstractPartitionAssignor
 from kafka.coordinator.assignors.sticky.partition_movements import PartitionMovements
 from kafka.coordinator.assignors.sticky.sorted_set import SortedSet
diff --git a/kafka/coordinator/consumer.py b/kafka/coordinator/consumer.py
index 36c91ee42..9c662ce7f 100644
--- a/kafka/coordinator/consumer.py
+++ b/kafka/coordinator/consumer.py
@@ -796,7 +796,7 @@ def _handle_offset_fetch_response(self, future, response):
             elif error_type is Errors.GroupAuthorizationFailedError:
                 future.failure(error)
             else:
-                log.error("Unknown error fetching offsets for %s: %s", tp, error)
+                log.error("Unknown error fetching offsets: %s", error)
                 future.failure(error)
             return
 
diff --git a/kafka/metrics/metric_name.py b/kafka/metrics/metric_name.py
index b5acd1662..32a7e3a4b 100644
--- a/kafka/metrics/metric_name.py
+++ b/kafka/metrics/metric_name.py
@@ -93,7 +93,7 @@ def __eq__(self, other):
             return True
         if other is None:
             return False
-        return (type(self) == type(other) and
+        return (isinstance(self, type(other)) and
                 self.group == other.group and
                 self.name == other.name and
                 self.tags == other.tags)
diff --git a/kafka/metrics/quota.py b/kafka/metrics/quota.py
index 4d1b0d6cb..237edf841 100644
--- a/kafka/metrics/quota.py
+++ b/kafka/metrics/quota.py
@@ -34,7 +34,7 @@ def __hash__(self):
     def __eq__(self, other):
         if self is other:
             return True
-        return (type(self) == type(other) and
+        return (isinstance(self, type(other)) and
                 self.bound == other.bound and
                 self.is_upper_bound() == other.is_upper_bound())
 
diff --git a/kafka/producer/kafka.py b/kafka/producer/kafka.py
index 668387aac..2a70700c4 100644
--- a/kafka/producer/kafka.py
+++ b/kafka/producer/kafka.py
@@ -612,8 +612,8 @@ def send(self, topic, value=None, key=None, headers=None, partition=None, timest
 
             if headers is None:
                 headers = []
-            assert type(headers) == list
-            assert all(type(item) == tuple and len(item) == 2 and type(item[0]) == str and type(item[1]) == bytes for item in headers)
+            assert isinstance(headers, list)
+            assert all(isinstance(item, tuple) and len(item) == 2 and isinstance(item[0], str) and isinstance(item[1], bytes) for item in headers)
 
             message_size = self._estimate_size_in_bytes(key_bytes, value_bytes, headers)
             self._ensure_valid_record_size(message_size)
diff --git a/kafka/protocol/api_versions.py b/kafka/protocol/api_versions.py
index dc0aa588e..7e2e61251 100644
--- a/kafka/protocol/api_versions.py
+++ b/kafka/protocol/api_versions.py
@@ -1,5 +1,7 @@
 from __future__ import absolute_import
 
+from io import BytesIO
+
 from kafka.protocol.api import Request, Response
 from kafka.protocol.types import Array, Int16, Int32, Schema
 
diff --git a/kafka/protocol/commit.py b/kafka/protocol/commit.py
index 53c2466fe..a0439e7ef 100644
--- a/kafka/protocol/commit.py
+++ b/kafka/protocol/commit.py
@@ -1,7 +1,7 @@
 from __future__ import absolute_import
 
 from kafka.protocol.api import Request, Response
-from kafka.protocol.types import Array, Int8, Int16, Int32, Int64, Schema, String
+from kafka.protocol.types import Array, Int16, Int32, Int64, Schema, String
 
 
 class OffsetCommitResponse_v0(Response):
diff --git a/kafka/protocol/find_coordinator.py b/kafka/protocol/find_coordinator.py
index a68a23902..be5b45ded 100644
--- a/kafka/protocol/find_coordinator.py
+++ b/kafka/protocol/find_coordinator.py
@@ -1,7 +1,7 @@
 from __future__ import absolute_import
 
 from kafka.protocol.api import Request, Response
-from kafka.protocol.types import Array, Int8, Int16, Int32, Int64, Schema, String
+from kafka.protocol.types import Int8, Int16, Int32, Schema, String
 
 
 class FindCoordinatorResponse_v0(Response):
diff --git a/kafka/protocol/offset_for_leader_epoch.py b/kafka/protocol/offset_for_leader_epoch.py
index afe8284eb..8465588a3 100644
--- a/kafka/protocol/offset_for_leader_epoch.py
+++ b/kafka/protocol/offset_for_leader_epoch.py
@@ -4,7 +4,7 @@
 from kafka.protocol.types import Array, CompactArray, CompactString, Int16, Int32, Int64, Schema, String, TaggedFields
 
 
-class OffsetForLeaderEpochResponse_v0(Request):
+class OffsetForLeaderEpochResponse_v0(Response):
     API_KEY = 23
     API_VERSION = 0
     SCHEMA = Schema(
@@ -16,7 +16,7 @@ class OffsetForLeaderEpochResponse_v0(Request):
                 ('end_offset', Int64))))))
 
 
-class OffsetForLeaderEpochResponse_v1(Request):
+class OffsetForLeaderEpochResponse_v1(Response):
     API_KEY = 23
     API_VERSION = 1
     SCHEMA = Schema(
@@ -29,7 +29,7 @@ class OffsetForLeaderEpochResponse_v1(Request):
                 ('end_offset', Int64))))))
 
 
-class OffsetForLeaderEpochResponse_v2(Request):
+class OffsetForLeaderEpochResponse_v2(Response):
     API_KEY = 23
     API_VERSION = 2
     SCHEMA = Schema(
@@ -43,13 +43,13 @@ class OffsetForLeaderEpochResponse_v2(Request):
                 ('end_offset', Int64))))))
 
 
-class OffsetForLeaderEpochResponse_v3(Request):
+class OffsetForLeaderEpochResponse_v3(Response):
     API_KEY = 23
     API_VERSION = 3
     SCHEMA = OffsetForLeaderEpochResponse_v2.SCHEMA
 
 
-class OffsetForLeaderEpochResponse_v4(Request):
+class OffsetForLeaderEpochResponse_v4(Response):
     API_KEY = 23
     API_VERSION = 4
     SCHEMA = Schema(
diff --git a/kafka/protocol/sasl_authenticate.py b/kafka/protocol/sasl_authenticate.py
index 528bb3cc6..a2b9b1988 100644
--- a/kafka/protocol/sasl_authenticate.py
+++ b/kafka/protocol/sasl_authenticate.py
@@ -1,7 +1,7 @@
 from __future__ import absolute_import
 
 from kafka.protocol.api import Request, Response
-from kafka.protocol.types import Array, Bytes, Int16, Int64, Schema, String
+from kafka.protocol.types import Bytes, Int16, Int64, Schema, String
 
 
 class SaslAuthenticateResponse_v0(Response):
diff --git a/kafka/sasl/gssapi.py b/kafka/sasl/gssapi.py
index 1be3de4a4..60b658c77 100644
--- a/kafka/sasl/gssapi.py
+++ b/kafka/sasl/gssapi.py
@@ -1,5 +1,7 @@
 from __future__ import absolute_import
 
+import struct
+
 # needed for SASL_GSSAPI authentication:
 try:
     import gssapi
@@ -66,7 +68,7 @@ def receive(self, auth_bytes):
             # simply set QoP to 'auth' only (first octet). We reuse the max message size proposed
             # by the server
             message_parts = [
-                Int8.encode(self.SASL_QOP_AUTH & Int8.decode(io.BytesIO(msg[0:1]))),
+                struct.pack('>b', self.SASL_QOP_AUTH & struct.unpack('>b', msg[0:1])),
                 msg[:1],
                 self.auth_id.encode(),
             ]
diff --git a/test/test_admin.py b/test/test_admin.py
index 279f85abf..cdb74242e 100644
--- a/test/test_admin.py
+++ b/test/test_admin.py
@@ -6,7 +6,7 @@
 
 def test_config_resource():
     with pytest.raises(KeyError):
-        bad_resource = kafka.admin.ConfigResource('something', 'foo')
+        _bad_resource = kafka.admin.ConfigResource('something', 'foo')
     good_resource = kafka.admin.ConfigResource('broker', 'bar')
     assert good_resource.resource_type == kafka.admin.ConfigResourceType.BROKER
     assert good_resource.name == 'bar'
@@ -59,11 +59,11 @@ def test_acl_resource():
 
 def test_new_topic():
     with pytest.raises(IllegalArgumentError):
-        bad_topic = kafka.admin.NewTopic('foo', -1, -1)
+        _bad_topic = kafka.admin.NewTopic('foo', -1, -1)
     with pytest.raises(IllegalArgumentError):
-        bad_topic = kafka.admin.NewTopic('foo', 1, -1)
+        _bad_topic = kafka.admin.NewTopic('foo', 1, -1)
     with pytest.raises(IllegalArgumentError):
-        bad_topic = kafka.admin.NewTopic('foo', 1, 1, {1: [1, 1, 1]})
+        _bad_topic = kafka.admin.NewTopic('foo', 1, 1, {1: [1, 1, 1]})
     good_topic = kafka.admin.NewTopic('foo', 1, 2)
     assert good_topic.name == 'foo'
     assert good_topic.num_partitions == 1
diff --git a/test/test_admin_integration.py b/test/test_admin_integration.py
index bd2fd216e..2f6b76598 100644
--- a/test/test_admin_integration.py
+++ b/test/test_admin_integration.py
@@ -140,7 +140,7 @@ def test_describe_configs_invalid_broker_id_raises(kafka_admin_client):
     broker_id = "str"
 
     with pytest.raises(ValueError):
-        configs = kafka_admin_client.describe_configs([ConfigResource(ConfigResourceType.BROKER, broker_id)])
+        kafka_admin_client.describe_configs([ConfigResource(ConfigResourceType.BROKER, broker_id)])
 
 
 @pytest.mark.skipif(env_kafka_version() < (0, 11), reason='Describe consumer group requires broker >=0.11')
@@ -148,7 +148,7 @@ def test_describe_consumer_group_does_not_exist(kafka_admin_client):
     """Tests that the describe consumer group call fails if the group coordinator is not available
     """
     with pytest.raises(GroupCoordinatorNotAvailableError):
-        group_description = kafka_admin_client.describe_consumer_groups(['test'])
+        kafka_admin_client.describe_consumer_groups(['test'])
 
 
 @pytest.mark.skipif(env_kafka_version() < (0, 11), reason='Describe consumer group requires broker >=0.11')
diff --git a/test/test_cluster.py b/test/test_cluster.py
index b55bdc5ad..f0a2f83d6 100644
--- a/test/test_cluster.py
+++ b/test/test_cluster.py
@@ -1,8 +1,6 @@
 # pylint: skip-file
 from __future__ import absolute_import
 
-import pytest
-
 from kafka.cluster import ClusterMetadata
 from kafka.protocol.metadata import MetadataResponse
 
diff --git a/test/test_fetcher.py b/test/test_fetcher.py
index 7e948e3cb..479f6e22b 100644
--- a/test/test_fetcher.py
+++ b/test/test_fetcher.py
@@ -10,7 +10,7 @@
 
 from kafka.client_async import KafkaClient
 from kafka.consumer.fetcher import (
-    CompletedFetch, ConsumerRecord, Fetcher, NoOffsetForPartitionError
+    CompletedFetch, ConsumerRecord, Fetcher
 )
 from kafka.consumer.subscription_state import SubscriptionState
 import kafka.errors as Errors
diff --git a/test/test_object_conversion.py b/test/test_object_conversion.py
index 9b1ff2131..a48eb0601 100644
--- a/test/test_object_conversion.py
+++ b/test/test_object_conversion.py
@@ -207,7 +207,7 @@ def test_with_metadata_response():
     assert len(obj['topics']) == 2
     assert obj['topics'][0]['error_code'] == 0
     assert obj['topics'][0]['topic'] == 'testtopic1'
-    assert obj['topics'][0]['is_internal'] == False
+    assert obj['topics'][0]['is_internal'] is False
     assert len(obj['topics'][0]['partitions']) == 2
     assert obj['topics'][0]['partitions'][0]['error_code'] == 0
     assert obj['topics'][0]['partitions'][0]['partition'] == 0
@@ -224,7 +224,7 @@ def test_with_metadata_response():
 
     assert obj['topics'][1]['error_code'] == 0
     assert obj['topics'][1]['topic'] == 'other-test-topic'
-    assert obj['topics'][1]['is_internal'] == True
+    assert obj['topics'][1]['is_internal'] is True
     assert len(obj['topics'][1]['partitions']) == 1
     assert obj['topics'][1]['partitions'][0]['error_code'] == 0
     assert obj['topics'][1]['partitions'][0]['partition'] == 0
diff --git a/test/test_protocol.py b/test/test_protocol.py
index 6f94c74e1..d0cc7ed0a 100644
--- a/test/test_protocol.py
+++ b/test/test_protocol.py
@@ -2,8 +2,6 @@
 import io
 import struct
 
-import pytest
-
 from kafka.protocol.api import RequestHeader
 from kafka.protocol.fetch import FetchRequest, FetchResponse
 from kafka.protocol.find_coordinator import FindCoordinatorRequest
@@ -273,7 +271,7 @@ def test_decode_fetch_response_partial():
 
 def test_struct_unrecognized_kwargs():
     try:
-        mr = MetadataRequest[0](topicz='foo')
+        _mr = MetadataRequest[0](topicz='foo')
         assert False, 'Structs should not allow unrecognized kwargs'
     except ValueError:
         pass
@@ -331,6 +329,6 @@ def test_compact_data_structs():
     assert CompactBytes.decode(io.BytesIO(b'\x00')) is None
     enc = CompactBytes.encode(b'')
     assert enc == b'\x01'
-    assert CompactBytes.decode(io.BytesIO(b'\x01')) is b''
+    assert CompactBytes.decode(io.BytesIO(b'\x01')) == b''
     enc = CompactBytes.encode(b'foo')
     assert CompactBytes.decode(io.BytesIO(enc)) == b'foo'
diff --git a/test/test_sender.py b/test/test_sender.py
index 83a26cd39..3da1a9f42 100644
--- a/test/test_sender.py
+++ b/test/test_sender.py
@@ -5,7 +5,6 @@
 import io
 
 from kafka.client_async import KafkaClient
-from kafka.cluster import ClusterMetadata
 from kafka.metrics import Metrics
 from kafka.protocol.broker_api_versions import BROKER_API_VERSIONS
 from kafka.protocol.produce import ProduceRequest