Flake8 the code.fix-16

16 files changed, 161 insertions, 119 deletions

diff --git a/.travis.yml b/.travis.yml
index 035969a..b0627ed 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -11,6 +11,10 @@ matrix:
           dist: xenial
         - python: "3.8-dev"
           dist: xenial
+        - name: "flake8"
+          install: pip install flake8
+          script: flake8 src setup.py
+          after_success:
 install:
     - pip install -U pip setuptools
     - pip install -U coverage coverage-python-version coveralls
diff --git a/CHANGES.rst b/CHANGES.rst
index 559616d..6faa270 100644
--- a/CHANGES.rst
+++ b/CHANGES.rst
@@ -10,6 +10,8 @@
 - Fix test failures and deprecation warnings occurring when using Python 3.8a1.
   (`#15 <https://github.com/zopefoundation/zope.tales/pull/15>`_)
 
+- Flake8 the code.
+
 
 4.3 (2018-10-05)
 ================
diff --git a/setup.cfg b/setup.cfg
index 2a9acf1..c1e4c65 100644
--- a/setup.cfg
+++ b/setup.cfg
@@ -1,2 +1,5 @@
 [bdist_wheel]
 universal = 1
+
+[flake8]
+doctests = yes
diff --git a/setup.py b/setup.py
index 931a6bc..d8b3f5b 100644
--- a/setup.py
+++ b/setup.py
@@ -26,65 +26,68 @@ def read(*rnames):
     with open(os.path.join(os.path.dirname(__file__), *rnames)) as f:
         return f.read()
 
+
 TESTS_REQUIRE = [
     'zope.testing',
     'zope.testrunner',
 ]
 
-setup(name='zope.tales',
-      version='5.0.dev0',
-      author='Zope Foundation and Contributors',
-      author_email='zope-dev@zope.org',
-      description='Zope Template Application Language Expression Syntax '
-                  '(TALES)',
-      long_description=(
-          read('README.rst')
-          + '\n\n' +
-          read('CHANGES.rst')
-      ),
-      keywords="zope template xml tales",
-      classifiers=[
-          'Development Status :: 5 - Production/Stable',
-          'Environment :: Web Environment',
-          'Intended Audience :: Developers',
-          'License :: OSI Approved :: Zope Public License',
-          'Programming Language :: Python',
-          'Programming Language :: Python :: 2',
-          'Programming Language :: Python :: 2.7',
-          'Programming Language :: Python :: 3',
-          'Programming Language :: Python :: 3.5',
-          'Programming Language :: Python :: 3.6',
-          'Programming Language :: Python :: 3.7',
-          'Programming Language :: Python :: Implementation :: CPython',
-          'Programming Language :: Python :: Implementation :: PyPy',
-          'Natural Language :: English',
-          'Operating System :: OS Independent',
-          'Topic :: Internet :: WWW/HTTP',
-          'Framework :: Zope :: 3',
-      ],
-      url='https://github.com/zopefoundation/zope.tales',
-      license='ZPL 2.1',
-      packages=find_packages('src'),
-      package_dir={'': 'src'},
-      namespace_packages=['zope'],
-      python_requires='>=2.7,!=3.0.*,!=3.1.*,!=3.2.*,!=3.3.*,!=3.4.*',
-      extras_require={
-          'test': TESTS_REQUIRE,
-          'tal': [
-              'zope.tal',
-          ],
-          'docs': [
-              'Sphinx',
-              'repoze.sphinx.autointerface',
-              'zope.tal',
-          ],
-      },
-      install_requires=[
-          'setuptools',
-          'zope.interface',
-          'six',
-      ],
-      tests_require=TESTS_REQUIRE,
-      include_package_data=True,
-      zip_safe=False,
+
+setup(
+    name='zope.tales',
+    version='5.0.dev0',
+    author='Zope Foundation and Contributors',
+    author_email='zope-dev@zope.org',
+    description='Zope Template Application Language Expression Syntax '
+                '(TALES)',
+    long_description=(
+        read('README.rst')
+        + '\n\n' +
+        read('CHANGES.rst')
+    ),
+    keywords="zope template xml tales",
+    classifiers=[
+        'Development Status :: 5 - Production/Stable',
+        'Environment :: Web Environment',
+        'Intended Audience :: Developers',
+        'License :: OSI Approved :: Zope Public License',
+        'Programming Language :: Python',
+        'Programming Language :: Python :: 2',
+        'Programming Language :: Python :: 2.7',
+        'Programming Language :: Python :: 3',
+        'Programming Language :: Python :: 3.5',
+        'Programming Language :: Python :: 3.6',
+        'Programming Language :: Python :: 3.7',
+        'Programming Language :: Python :: Implementation :: CPython',
+        'Programming Language :: Python :: Implementation :: PyPy',
+        'Natural Language :: English',
+        'Operating System :: OS Independent',
+        'Topic :: Internet :: WWW/HTTP',
+        'Framework :: Zope :: 3',
+    ],
+    url='https://github.com/zopefoundation/zope.tales',
+    license='ZPL 2.1',
+    packages=find_packages('src'),
+    package_dir={'': 'src'},
+    namespace_packages=['zope'],
+    python_requires='>=2.7,!=3.0.*,!=3.1.*,!=3.2.*,!=3.3.*,!=3.4.*',
+    extras_require={
+        'test': TESTS_REQUIRE,
+        'tal': [
+            'zope.tal',
+        ],
+        'docs': [
+            'Sphinx',
+            'repoze.sphinx.autointerface',
+            'zope.tal',
+        ],
+    },
+    install_requires=[
+        'setuptools',
+        'zope.interface',
+        'six',
+    ],
+    tests_require=TESTS_REQUIRE,
+    include_package_data=True,
+    zip_safe=False,
 )
diff --git a/src/zope/tales/__init__.py b/src/zope/tales/__init__.py
index 61cfd4c..ccf848b 100644
--- a/src/zope/tales/__init__.py
+++ b/src/zope/tales/__init__.py
@@ -13,4 +13,3 @@
 ##############################################################################
 """Template Attribute Language - Expression Syntax
 """
-
diff --git a/src/zope/tales/engine.py b/src/zope/tales/engine.py
index 7bab8f2..dd07600 100644
--- a/src/zope/tales/engine.py
+++ b/src/zope/tales/engine.py
@@ -24,6 +24,7 @@ from zope.tales.expressions import LazyExpr
 from zope.tales.expressions import SimpleModuleImporter
 from zope.tales.pythonexpr import PythonExpr
 
+
 def DefaultEngine():
     """
     Create and return an instance of :class:`~.ExpressionEngine` (an
@@ -44,8 +45,9 @@ def DefaultEngine():
     ``modules``
         :class:`.SimpleModuleImporter`
 
-    In addition, the default ``path`` expressions (``standard``, ``path``, ``exists``
-    and ``nocall``), all implemented by :class:`.PathExpr`, are registered.
+    In addition, the default ``path`` expressions (``standard``, ``path``,
+    ``exists`` and ``nocall``), all implemented by :class:`.PathExpr`, are
+    registered.
     """
     e = ExpressionEngine()
     reg = e.registerType
@@ -59,4 +61,5 @@ def DefaultEngine():
     e.registerBaseName('modules', SimpleModuleImporter())
     return e
 
+
 Engine = DefaultEngine()
diff --git a/src/zope/tales/expressions.py b/src/zope/tales/expressions.py
index 48be495..81a626b 100644
--- a/src/zope/tales/expressions.py
+++ b/src/zope/tales/expressions.py
@@ -16,9 +16,9 @@ Basic Page Template expression types.
 
 Expression objects are created by the :class:`.ExpressionEngine`
 (they must have previously been registered with
-:func:`~zope.tales.tales.ExpressionEngine.registerType`).  The expression object itself
-is a callable object taking one argument, *econtext*, which is the local
-expression namespace.
+:func:`~zope.tales.tales.ExpressionEngine.registerType`).  The expression
+object itself is a callable object taking one argument, *econtext*, which is
+the local expression namespace.
 
 """
 import re
@@ -38,6 +38,7 @@ namespace_re = re.compile(r'(\w+):(.+)')
 
 PY2 = sys.version_info[0] == 2
 
+
 def simpleTraverse(object, path_items, econtext):
     """Traverses a sequence of names, first trying attributes then items.
     """
@@ -168,7 +169,7 @@ class PathExpr(object):
         'path',
         'exists',
         'nocall',
-        )
+    )
 
     def __init__(self, name, expr, engine, traverser=simpleTraverse):
         self._s = expr
@@ -240,11 +241,11 @@ class PathExpr(object):
         return '<PathExpr %s:%s>' % (self._name, repr(self._s))
 
 
-
 _interp = re.compile(
     r'\$(%(n)s)|\${(%(n)s(?:/[^}|]*)*(?:\|%(n)s(?:/[^}|]*)*)*)}'
     % {'n': NAME_RE})
 
+
 @implementer(ITALESExpression)
 class StringExpr(object):
     """
@@ -264,7 +265,8 @@ class StringExpr(object):
             path_type = engine.getTypes()['path']
             parts = []
             for exp in expr.split('$$'):
-                if parts: parts.append('$')
+                if parts:
+                    parts.append('$')
                 m = _interp.search(exp)
                 while m is not None:
                     parts.append(exp[:m.start()])
@@ -365,6 +367,7 @@ class LazyWrapper(DeferWrapper):
             self._result = r = self._expr(self._econtext)
         return r
 
+
 class LazyExpr(DeferExpr):
     """
     An expression that will defer evaluation of its
diff --git a/src/zope/tales/interfaces.py b/src/zope/tales/interfaces.py
index 158b794..58c234f 100644
--- a/src/zope/tales/interfaces.py
+++ b/src/zope/tales/interfaces.py
@@ -33,6 +33,7 @@ class ITALESFunctionNamespace(Interface):
     def setEngine(engine):
         """Sets the engine that is used to evaluate TALES expressions."""
 
+
 class ITALESExpression(Interface):
     """TALES expression
 
@@ -46,6 +47,7 @@ class ITALESExpression(Interface):
         *econtext* and return computed value.
         """
 
+
 class ITALESIterator(ITALIterator):
     """TAL Iterator provided by TALES.
 
diff --git a/src/zope/tales/pythonexpr.py b/src/zope/tales/pythonexpr.py
index 3f47bed..01df726 100644
--- a/src/zope/tales/pythonexpr.py
+++ b/src/zope/tales/pythonexpr.py
@@ -14,6 +14,7 @@
 """Generic Python Expression Handler
 """
 
+
 class PythonExpr(object):
     """
     Evaluates a python expression by calling :func:`eval` after
@@ -25,8 +26,8 @@ class PythonExpr(object):
         :param ExpressionEngine engine: The expression compiler that
             is creating us.
         """
-        text = '\n'.join(expr.splitlines()) # normalize line endings
-        text = '(' + text + ')' # Put text in parens so newlines don't matter
+        text = '\n'.join(expr.splitlines())  # normalize line endings
+        text = '(' + text + ')'  # Put text in parens so newlines don't matter
         self.text = text
         try:
             code = self._compile(text, '<string>')
diff --git a/src/zope/tales/tales.py b/src/zope/tales/tales.py
index 21a3276..d5ca006 100644
--- a/src/zope/tales/tales.py
+++ b/src/zope/tales/tales.py
@@ -15,7 +15,6 @@
 
 An implementation of a TAL expression engine
 """
-__docformat__ = "reStructuredText"
 import re
 
 try:
@@ -29,23 +28,28 @@ import six
 
 from zope.tales.interfaces import ITALESIterator
 
+
 class ITALExpressionEngine(Interface):
     pass
+
+
 class ITALExpressionCompiler(Interface):
     pass
+
+
 class ITALExpressionErrorInfo(Interface):
     pass
 
+
 try:
     # Override with real, if present
-    from zope.tal.interfaces import (ITALExpressionEngine,
+    from zope.tal.interfaces import (ITALExpressionEngine,  # noqa: F811
                                      ITALExpressionCompiler,
                                      ITALExpressionErrorInfo)
 except ImportError:
     pass
 
 
-
 NAME_RE = r"[a-zA-Z][a-zA-Z0-9_]*"
 _parse_expr = re.compile(r"(%s):" % NAME_RE).match
 _valid_name = re.compile('%s$' % NAME_RE).match
@@ -54,18 +58,22 @@ _valid_name = re.compile('%s$' % NAME_RE).match
 class TALESError(Exception):
     """Error during TALES evaluation"""
 
+
 class Undefined(TALESError):
-    '''Exception raised on traversal of an undefined path'''
+    """Exception raised on traversal of an undefined path."""
+
 
 class CompilerError(Exception):
-    '''TALES Compiler Error'''
+    """TALES Compiler Error"""
+
 
 class RegistrationError(Exception):
-    '''Expression type or base name registration Error'''
+    """Expression type or base name registration Error."""
 
 
 _default = object()
 
+
 @implementer(ITALESIterator)
 class Iterator(object):
     """
@@ -568,8 +576,8 @@ class ExpressionEngine(object):
         :param str namespace: a string containing the name of the namespace to
             be registered
 
-        :param callable namespacecallable: a callable object which takes the following
-            parameter:
+        :param callable namespacecallable: a callable object which takes the
+            following parameter:
 
             :context: the object on which the functions
                     provided by this namespace will
@@ -596,7 +604,6 @@ class ExpressionEngine(object):
         """
         self.namespaces[namespacename] = namespacecallable
 
-
     def getFunctionNamespace(self, namespacename):
         """ Returns the function namespace """
         return self.namespaces[namespacename]
@@ -605,11 +612,12 @@ class ExpressionEngine(object):
         """
         Register an expression of *name* to be handled with *handler*.
 
-        :raises RegistrationError: If this is a duplicate registration for *name*,
-            or if *name* is not a valid expression type name.
+        :raises RegistrationError: If this is a duplicate registration for
+            *name*, or if *name* is not a valid expression type name.
         """
         if not _valid_name(name):
-            raise RegistrationError('Invalid expression type name "%s".' % name)
+            raise RegistrationError(
+                'Invalid expression type name "%s".' % name)
         types = self.types
         if name in types:
             raise RegistrationError(
@@ -674,8 +682,8 @@ class Context(object):
     :class:`zope.tal.interfaces.ITALExpressionEngine`.
 
     This class is called ``Context`` because an instance of this class
-    holds context information (namespaces) that it uses when evaluating compiled
-    expressions.
+    holds context information (namespaces) that it uses when evaluating
+    compiled expressions.
     """
     position = (None, None)
     source_file = None
@@ -695,7 +703,7 @@ class Context(object):
         self.repeat_vars = rv = {}
         # Wrap this, as it is visible to restricted code
         self.setContext('repeat', rv)
-        self.setContext('loop', rv) # alias
+        self.setContext('loop', rv)  # alias
 
         self.vars = vars = contexts.copy()
         self._vars_stack = [vars]
@@ -704,7 +712,8 @@ class Context(object):
         self._scope_stack = []
 
     def setContext(self, name, value):
-        """Hook to allow subclasses to do things like adding security proxies."""
+        """Hook to allow subclasses to do things like adding security proxies.
+        """
         self.contexts[name] = value
 
     def beginScope(self):
@@ -822,7 +831,7 @@ class TALESTracebackSupplement(object):
         import pprint
         data = self.context.contexts.copy()
         if 'modules' in data:
-            del data['modules'] # the list is really long and boring
+            del data['modules']  # the list is really long and boring
         s = pprint.pformat(data)
         if not as_html:
             return '   - Names:\n      %s' % s.replace('\n', '\n      ')
diff --git a/src/zope/tales/tests/simpleexpr.py b/src/zope/tales/tests/simpleexpr.py
index 7befa35..ac5409c 100644
--- a/src/zope/tales/tests/simpleexpr.py
+++ b/src/zope/tales/tests/simpleexpr.py
@@ -14,15 +14,16 @@
 """Simple TALES Expression
 """
 
+
 class SimpleExpr(object):
-    '''Simple example of an expression type handler
+    """Simple example of an expression type handler for testing."""
 
-    for testing
-    '''
     def __init__(self, name, expr, engine):
         self._name = name
         self._expr = expr
+
     def __call__(self, econtext):
         return self._name, self._expr
+
     def __repr__(self):
         return '<SimpleExpr %s %s>' % (self._name, repr(self._expr))
diff --git a/src/zope/tales/tests/test_expressions.py b/src/zope/tales/tests/test_expressions.py
index 94f8ecf..651ed74 100644
--- a/src/zope/tales/tests/test_expressions.py
+++ b/src/zope/tales/tests/test_expressions.py
@@ -32,8 +32,8 @@ class Data(object):
         self.__dict__.update(kw)
 
     def __getattr__(self, name):
-        # Let linters (like pylint) know this is a dynamic class and they shouldn't
-        # emit "Data has no attribute" errors
+        # Let linters (like pylint) know this is a dynamic class and they
+        # shouldn't emit "Data has no attribute" errors
         return object.__getattribute__(self, name)
 
     def __repr__(self):
@@ -41,6 +41,7 @@ class Data(object):
 
     __str__ = __repr__
 
+
 class ErrorGenerator(object):
 
     def __getitem__(self, name):
@@ -51,15 +52,17 @@ class ErrorGenerator(object):
             e = getattr(builtins, name, None) or SystemError
         raise e('mess')
 
+
 class Callable(object):
 
     def __call__(self):
         return 42
 
-class OldStyleCallable: # NOT object
 
+class OldStyleCallable:  # NOT object
     pass
 
+
 class ExpressionTestBase(zope.tales.tests.TestCase):
 
     def setUp(self):
@@ -220,7 +223,8 @@ class TestParsedExpressions(ExpressionTestBase):
         # Simple eight bit string interpolation should just work.
         # Except on Py3, where we really mess it up.
         expr = self.engine.compile('string:a ${eightBits}')
-        expected = 'a ' + self.context.vars['eightBits'] if not six.PY3 else self.py3BrokenEightBits
+        expected = ('a ' + self.context.vars['eightBits']
+                    if not six.PY3 else self.py3BrokenEightBits)
         self._check_evals_to(expr, expected)
 
     def testStringUnicode(self):
@@ -241,7 +245,8 @@ class TestParsedExpressions(ExpressionTestBase):
             # poorly.
             self.assertTrue(six.PY3)
             self.assertEqual(result, self.py3BrokenEightBits)
-            self.context.vars['eightBits'].decode('ascii') # raise UnicodeDecodeError
+            # raise UnicodeDecodeError
+            self.context.vars['eightBits'].decode('ascii')
 
     def test_string_escape_percent(self):
         self._check_evals_to('string:%', '%')
@@ -283,6 +288,7 @@ class TestParsedExpressions(ExpressionTestBase):
 
     def testEmptyPathSegmentRaisesCompilerError(self):
         CompilerError = self.engine.getCompilerError()
+
         def check(expr):
             self.assertRaises(CompilerError, self.engine.compile, expr)
 
@@ -394,7 +400,7 @@ class FunctionTests(ExpressionTestBase):
         self.engine.registerFunctionNamespace('namespace', self.TestNameSpace)
         self.engine.registerFunctionNamespace('not_callable_ns', None)
 
-    ## framework-ish tests
+    # framework-ish tests
 
     def testSetEngine(self):
         expr = self.engine.compile('adapterTest/namespace:engine')
@@ -411,7 +417,7 @@ class FunctionTests(ExpressionTestBase):
                           self.engine.getFunctionNamespace,
                           'badnamespace')
 
-    ## compile time tests
+    # compile time tests
 
     def testBadNamespace(self):
         # namespace doesn't exist
@@ -457,14 +463,15 @@ class FunctionTests(ExpressionTestBase):
         e = exc.exception
         self.assertEqual(e.args[0], 'title')
 
-    ## runtime tests
+    # runtime tests
 
     def testNormalFunction(self):
         expr = self.engine.compile('adapterTest/namespace:upper')
         self.assertEqual(expr(self.context), 'YIKES')
 
     def testFunctionOnFunction(self):
-        expr = self.engine.compile('adapterTest/namespace:jump/namespace:upper')
+        expr = self.engine.compile(
+            'adapterTest/namespace:jump/namespace:upper')
         self.assertEqual(expr(self.context), 'XANDER')
 
     def testPathOnFunction(self):
@@ -476,6 +483,7 @@ class FunctionTests(ExpressionTestBase):
         with self.assertRaisesRegex(ValueError, 'None'):
             expr(self.context)
 
+
 class TestSimpleModuleImporter(unittest.TestCase):
 
     def _makeOne(self):
@@ -493,7 +501,6 @@ class TestSimpleModuleImporter(unittest.TestCase):
         with self.assertRaises(ImportError):
             self._makeOne()['this cannot exist']
 
-
     def test_no_such_submodule_not_package(self):
         with self.assertRaises(ImportError):
             self._makeOne()['zope.tales.tests.test_expressions.submodule']
diff --git a/src/zope/tales/tests/test_pythonexpr.py b/src/zope/tales/tests/test_pythonexpr.py
index 7410c41..edc8764 100644
--- a/src/zope/tales/tests/test_pythonexpr.py
+++ b/src/zope/tales/tests/test_pythonexpr.py
@@ -20,6 +20,7 @@ from zope.tales.tales import Context
 from zope.tales.pythonexpr import PythonExpr
 from zope.tales.pythonexpr import ExprTypeProxy
 
+
 class TestPythonExpr(unittest.TestCase):
 
     def setUp(self):
diff --git a/src/zope/tales/tests/test_tales.py b/src/zope/tales/tests/test_tales.py
index 1781624..03a1fe5 100644
--- a/src/zope/tales/tests/test_tales.py
+++ b/src/zope/tales/tests/test_tales.py
@@ -16,6 +16,7 @@
 from doctest import DocTestSuite
 import unittest
 import re
+import sys
 
 import six
 from zope.tales import tales
@@ -52,6 +53,7 @@ class TestIterator(unittest.TestCase):
         self.assertTrue(not next(it), "Multi-element iterator")
         context._complete_()
 
+
 class TALESTests(unittest.TestCase):
 
     def testRegisterType(self):
@@ -150,6 +152,7 @@ class TALESTests(unittest.TestCase):
 
         ctxt.endScope()
 
+
 class TestExpressionEngine(zope.tales.tests.TestCase):
 
     def setUp(self):
@@ -183,6 +186,7 @@ class TestExpressionEngine(zope.tales.tests.TestCase):
         self.assertEqual(ctx.contexts['b'], 2)
         self.assertEqual(ctx.contexts['c'], 1)
 
+
 class TestContext(unittest.TestCase):
 
     def setUp(self):
@@ -249,7 +253,6 @@ class TestContext(unittest.TestCase):
         self.assertEqual(u'text', self.context.evaluateText("it"))
 
     def test_traceback_supplement(self):
-        import sys
         def raises(self):
             raise Exception()
 
@@ -305,6 +308,7 @@ class Harness(object):
     def __getattr__(self, name):
         return HarnessMethod(self, name)
 
+
 class HarnessMethod(object):
 
     def __init__(self, harness, name):
@@ -333,11 +337,10 @@ class HarnessMethod(object):
 
 
 def test_suite():
-    checker = renormalizing.RENormalizing(
-        [(re.compile(r"object of type 'MyIter' has no len\(\)"),
-          r"len() of unsized object"),
-        ]
-    )
+    checker = renormalizing.RENormalizing([
+        (re.compile(r"object of type 'MyIter' has no len\(\)"),
+         r"len() of unsized object"),
+    ])
     suite = unittest.defaultTestLoader.loadTestsFromName(__name__)
     suite.addTest(DocTestSuite("zope.tales.tales",
                                checker=checker))
diff --git a/src/zope/tales/tests/test_traverser.py b/src/zope/tales/tests/test_traverser.py
index b791889..dd9eb0d 100644
--- a/src/zope/tales/tests/test_traverser.py
+++ b/src/zope/tales/tests/test_traverser.py
@@ -13,7 +13,7 @@
 ##############################################################################
 """ Tests for zope.tales.expressions.simpleTraverse
 """
-from unittest import TestCase, TestSuite, makeSuite, main
+from unittest import TestCase
 from zope.tales.expressions import simpleTraverse
 
 
@@ -21,13 +21,16 @@ class AttrTraversable(object):
     """Traversable by attribute access"""
     attr = 'foo'
 
+
 class ItemTraversable(object):
     """Traversable by item access"""
+
     def __getitem__(self, name):
         if name == 'attr':
             return 'foo'
         raise KeyError(name)
 
+
 class AllTraversable(AttrTraversable, ItemTraversable):
     """Traversable by attribute and item access"""
     pass
@@ -35,6 +38,7 @@ class AllTraversable(AttrTraversable, ItemTraversable):
 
 _marker = object()
 
+
 def getitem(ob, name, default=_marker):
     """Helper a la getattr(ob, name, default)."""
     try:
@@ -82,7 +86,7 @@ class TraverserTests(TestCase):
         self.assertRaises(KeyError, getitem, ob, 'missing_attr')
 
     def testTraverseEmptyPath(self):
-        # simpleTraverse should return the original object if the path is emtpy
+        # simpleTraverse should return the original object if the path is empty
         ob = object()
         self.assertEqual(simpleTraverse(ob, [], None), ob)
 
@@ -95,7 +99,8 @@ class TraverserTests(TestCase):
         # simpleTraverse should raise AttributeError
         ob = AttrTraversable()
         # Here lurks the bug (unexpected NamError raised)
-        self.assertRaises(AttributeError, simpleTraverse, ob, ['missing_attr'], None)
+        self.assertRaises(
+            AttributeError, simpleTraverse, ob, ['missing_attr'], None)
 
     def testTraverseByItem(self):
         # simpleTraverse should find attr through item access
@@ -113,17 +118,7 @@ class TraverserTests(TestCase):
         self.assertEqual(simpleTraverse(ob, ['attr'], None), 'foo')
 
     def testTraverseByMissingAll(self):
-        # simpleTraverse should raise KeyError (because ob implements __getitem__)
+        # simpleTraverse should raise KeyError (because ob implements
+        # __getitem__)
         ob = AllTraversable()
         self.assertRaises(KeyError, simpleTraverse, ob, ['missing_attr'], None)
-
-
-def test_suite():
-    return TestSuite((
-        makeSuite(TraverserTests),
-    ))
-
-
-if __name__ == '__main__':
-    main(defaultTest='test_suite')
-
diff --git a/tox.ini b/tox.ini
index 8929592..5413964 100644
--- a/tox.ini
+++ b/tox.ini
@@ -1,6 +1,6 @@
 [tox]
 envlist =
-    py27,py35,py36,py37,py38,pypy,pypy3,coverage,docs
+    flake8,py27,py35,py36,py37,py38,pypy,pypy3,coverage,docs
 
 [testenv]
 commands =
@@ -28,3 +28,9 @@ commands =
 deps =
     {[testenv]deps}
     .[docs]
+
+
+[testenv:flake8]
+deps = flake8
+skipinstall = true
+commands = flake8 setup.py src