diff --git a/google/auth/_oauth2client.py b/google/auth/_oauth2client.py
index e298fb1..71fd7bf 100644
--- a/google/auth/_oauth2client.py
+++ b/google/auth/_oauth2client.py
@@ -21,19 +21,20 @@
 
 from __future__ import absolute_import
 
+import six
+
 from google.auth import _helpers
 import google.auth.app_engine
 import google.oauth2.credentials
 import google.oauth2.service_account
 
-import six
 try:
     import oauth2client.client
     import oauth2client.contrib.gce
     import oauth2client.service_account
 except ImportError as caught_exc:
-    new_exc = ImportError('oauth2client is not installed.')
-    six.raise_from(new_exc, caught_exc)
+    six.raise_from(
+        ImportError('oauth2client is not installed.'), caught_exc)
 
 try:
     import oauth2client.contrib.appengine
diff --git a/google/auth/transport/grpc.py b/google/auth/transport/grpc.py
index 08b2f57..0d44f64 100644
--- a/google/auth/transport/grpc.py
+++ b/google/auth/transport/grpc.py
@@ -20,10 +20,13 @@
 try:
     import grpc
 except ImportError as caught_exc:  # pragma: NO COVER
-    new_exc = ImportError(
-        'gRPC is not installed, please install the grpcio package to use the '
-        'gRPC transport.')
-    six.raise_from(new_exc, caught_exc)
+    six.raise_from(
+        ImportError(
+            'gRPC is not installed, please install the grpcio package '
+            'to use the gRPC transport.'
+        ),
+        caught_exc,
+    )
 
 
 class AuthMetadataPlugin(grpc.AuthMetadataPlugin):
diff --git a/google/auth/transport/requests.py b/google/auth/transport/requests.py
index 31ce22d..66ff0d3 100644
--- a/google/auth/transport/requests.py
+++ b/google/auth/transport/requests.py
@@ -18,15 +18,19 @@
 
 import logging
 
-import six
 try:
     import requests
 except ImportError as caught_exc:  # pragma: NO COVER
-    new_exc = ImportError(
-        'The requests library is not installed, please install the requests '
-        'package to use the requests transport.')
-    six.raise_from(new_exc, caught_exc)
-import requests.exceptions
+    import six
+    six.raise_from(
+        ImportError(
+            'The requests library is not installed, please install the '
+            'requests package to use the requests transport.'
+        ),
+        caught_exc,
+    )
+import requests.exceptions  # pylint: disable=ungrouped-imports
+import six  # pylint: disable=ungrouped-imports
 
 from google.auth import exceptions
 from google.auth import transport
diff --git a/google/auth/transport/urllib3.py b/google/auth/transport/urllib3.py
index 872bf9f..ec20fb6 100644
--- a/google/auth/transport/urllib3.py
+++ b/google/auth/transport/urllib3.py
@@ -30,15 +30,19 @@
 except ImportError:  # pragma: NO COVER
     certifi = None
 
-import six
 try:
     import urllib3
 except ImportError as caught_exc:  # pragma: NO COVER
-    new_exc = ImportError(
-        'The urllib3 library is not installed, please install the urllib3 '
-        'package to use the urllib3 transport.')
-    six.raise_from(new_exc, caught_exc)
-import urllib3.exceptions
+    import six
+    six.raise_from(
+        ImportError(
+            'The urllib3 library is not installed, please install the '
+            'urllib3 package to use the urllib3 transport.'
+        ),
+        caught_exc,
+    )
+import six
+import urllib3.exceptions  # pylint: disable=ungrouped-imports
 
 from google.auth import exceptions
 from google.auth import transport
diff --git a/tests/compute_engine/test_credentials.py b/tests/compute_engine/test_credentials.py
index ee343fe..c78511b 100644
--- a/tests/compute_engine/test_credentials.py
+++ b/tests/compute_engine/test_credentials.py
@@ -75,7 +75,7 @@
     def test_refresh_error(self, get):
         get.side_effect = exceptions.TransportError('http error')
 
-        with pytest.raises(exceptions.RefreshError) as excinfo:
+        with pytest.raises(exceptions.RefreshError):
             self.credentials.refresh(None)
 
     @mock.patch('google.auth.compute_engine._metadata.get', autospec=True)