ci: added flake8 linter

addresses reanahub#456

.flake8

@@ -0,0 +1,20 @@
+[flake8]
+max-line-length = 89
+
+exclude =
+    build
+    modules
+    dist
+    docs
+    coverage.xml
+    reana_job_controller.egg-info
+    .*/
+    env/
+    .git
+    __pycache__
+
+ignore = E203, E231, E266, E501, W503, F403, F401
+
+max-complexity = 18
+
+select = B,C,E,F,W,T4,B9

.github/workflows/ci.yml

@@ -36,6 +36,23 @@ jobs:
           pip install black==19.10b0
           ./run-tests.sh --check-black
 
+  lint-flake8:
+    runs-on: ubuntu-20.04
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v2
+
+      - name: Setup Python
+        uses: actions/setup-python@v2
+        with:
+          python-version: 3.8
+
+      - name: Check compliance with pep8, pyflakes and circular complexity
+        run: |
+          pip install --upgrade pip
+          pip install flake8
+          ./run-tests.sh --check-flake8
+
   lint-pydocstyle:
     runs-on: ubuntu-20.04
     steps:

MANIFEST.in

@@ -11,6 +11,7 @@ include *.html
 include *.yaml
 include *.yml
 include *.sh
+include .flake8
 include pytest.ini
 prune docs/_build
 recursive-include reana *.py

run-tests.sh

@@ -20,6 +20,10 @@ check_black () {
     black --check .
 }
 
+check_flake8 () {
+    flake8 .
+}
+
 check_pydocstyle () {
     pydocstyle reana
 }
@@ -43,6 +47,7 @@ check_helm () {
 check_all () {
     check_script
     check_black
+    check_flake8
     check_pydocstyle
     check_manifest
     check_sphinx
@@ -60,6 +65,7 @@ do
     case $arg in
         --check-shellscript) check_script;;
         --check-black) check_black;;
+        --check-flake8) check_flake8;;
         --check-pydocstyle) check_pydocstyle;;
         --check-manifest) check_manifest;;
         --check-sphinx) check_sphinx;;

setup.py

@@ -52,7 +52,7 @@
 
 # Get the version string. Cannot be done with import!
 with open(os.path.join("reana", "version.py"), "rt") as f:
-    version = re.search('__version__\s*=\s*"(?P<version>.*)"\n', f.read()).group(
+    version = re.search(r'__version__\s*=\s*"(?P<version>.*)"\n', f.read()).group(
         "version"
     )
 

tests/benchmark/locustfile.py

@@ -65,12 +65,12 @@ def setup(self):
     @task
     def ping(self):
         """Ping reana instance."""
-        self.client.get(f"/api/ping")
+        self.client.get("/api/ping")
 
     @task
     def get_worflows(self):
         """Get workflows."""
-        self.client.get(f"/api/workflows", params=(("access_token", TOKEN),))
+        self.client.get("/api/workflows", params=(("access_token", TOKEN),))
 
     @task
     def get_worflow_logs(self):