Add pytest-flake8

.flake8

@@ -0,0 +1,15 @@
+[flake8]
+max-line-length = 99
+ignore = W503
+exclude =
+    .git
+    .tox
+    venv*
+
+    # pending revision
+    cssselect/__init__.py
+    cssselect/parser.py
+    cssselect/xpath.py
+    docs/conf.py
+    setup.py
+    tests/test_cssselect.py

.github/workflows/checks.yml

@@ -7,6 +7,9 @@ jobs:
     strategy:
       matrix:
         include:
+        - python-version: 3
+          env:
+            TOXENV: flake8
         - python-version: 3
           env:
             TOXENV: security

tox.ini

@@ -1,15 +1,21 @@
 [tox]
-envlist = security,py
+envlist = flake8,security,py
 
 [testenv]
+basepython = python3
 deps=
     -r tests/requirements.txt
-
 commands =
     py.test --cov-report term --cov=cssselect
 
+[testenv:flake8]
+deps =
+    flake8==3.9.2
+commands =
+    flake8 {posargs: cssselect setup.py tests docs/conf.py}
+
 [testenv:security]
 deps =
     bandit
 commands =
-    bandit -r -c .bandit.yml {posargs:cssselect}
+    bandit -r -c .bandit.yml {posargs: cssselect}