diff --git a/setup_validate.py b/setup_validate.py
index 72e9a21..708133d 100644
--- a/setup_validate.py
+++ b/setup_validate.py
@@ -11,7 +11,6 @@
 # This software is licensed under the terms of the BSD license.
 # http://opensource.org/licenses/BSD-3-Clause
 
-import sys
 from distutils.core import setup
 from validate import __version__ as VERSION
 
diff --git a/src/configobj/__init__.py b/src/configobj/__init__.py
index 3f91127..a8fd7ad 100644
--- a/src/configobj/__init__.py
+++ b/src/configobj/__init__.py
@@ -297,7 +297,7 @@ def __init__(self, section):
 
     def interpolate(self, key, value):
         # short-cut
-        if not self._cookie in value:
+        if self._cookie not in value:
             return value
         
         def recursive_interpolate(key, value, section, backtrail):
@@ -2237,7 +2237,7 @@ def validate_entry(entry, spec, val, missing, ret_true, ret_false):
             if entry in ('__many__', '___many___'):
                 # reserved names
                 continue
-            if (not entry in section.scalars) or (entry in section.defaults):
+            if (entry not in section.scalars) or (entry in section.defaults):
                 # missing entries
                 # or entries from defaults
                 missing = True
diff --git a/src/configobj/validate.py b/src/configobj/validate.py
index 5eb7ab4..2901002 100644
--- a/src/configobj/validate.py
+++ b/src/configobj/validate.py
@@ -163,7 +163,7 @@
 
 import re
 import sys
-from pprint import pprint
+from pprint import pprint  # noqa: F401  (used in doctests)
 
 
 _list_arg = re.compile(r'''
@@ -264,7 +264,8 @@ def dottedQuadToNum(ip):
     """
     
     # import here to avoid it when ip_addr values are not used
-    import socket, struct
+    import socket
+    import struct
     
     try:
         return struct.unpack('!L',
@@ -314,7 +315,8 @@ def numToDottedQuad(num):
     """
     
     # import here to avoid it when ip_addr values are not used
-    import socket, struct
+    import socket
+    import struct
     
     # no need to intercept here, 4294967295L is fine
     if num > int(4294967295) or num < 0:
@@ -653,7 +655,7 @@ def _parse_check(self, check):
                 keymatch = self._key_arg.match(arg)
                 if keymatch:
                     val = keymatch.group(2)
-                    if not val in ("'None'", '"None"'):
+                    if val not in ("'None'", '"None"'):
                         # Special case a quoted None
                         val = self._unquote(val)
                     fun_kwargs[keymatch.group(1)] = val
@@ -740,7 +742,7 @@ def _is_num_param(names, values, to_float=False):
         elif isinstance(val, (int, float, str)):
             try:
                 out_params.append(fun(val))
-            except ValueError as e:
+            except ValueError:
                 raise VdtParamError(name, val)
         else:
             raise VdtParamError(name, val)
@@ -1301,7 +1303,7 @@ def is_option(value, *options):
     """
     if not isinstance(value, str):
         raise VdtTypeError(value)
-    if not value in options:
+    if value not in options:
         raise VdtValueError(value)
     return value
 
diff --git a/src/tests/configobj_doctests.py b/src/tests/configobj_doctests.py
index 5a44d49..71d3c8f 100644
--- a/src/tests/configobj_doctests.py
+++ b/src/tests/configobj_doctests.py
@@ -15,13 +15,10 @@
 # https://github.com/DiffSK/configobj
 
 import sys
-
-from io import StringIO
-
-import sys
+from io import StringIO  # noqa: F401  (used in doctests)
 
 from configobj import *
-from configobj.validate import Validator
+from configobj.validate import Validator  # noqa: F401  (used in doctests)
 
 
 def _test_validate():
diff --git a/src/tests/test_validate.py b/src/tests/test_validate.py
index 2d72821..71956fb 100644
--- a/src/tests/test_validate.py
+++ b/src/tests/test_validate.py
@@ -2,7 +2,7 @@
 
 from configobj import ConfigObj
 import pytest
-from configobj.validate import Validator, VdtValueTooSmallError
+from configobj.validate import VdtValueTooSmallError
 
 
 class TestImporting(object):