Linters. Pylint. (#2816)

* Linters. Pylint.

* Pylint. Apply comments.

.github/workflows/pylint.yml

@@ -0,0 +1,44 @@
+name: Linter
+on: pull_request
+jobs:
+  PyLint:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+      - id: files
+        uses: jitterbit/get-changed-files@v1
+
+      - name: Run checks
+        run: |
+          for files in ${{ steps.files.outputs.added_modified }}; do
+            extension="${files##*.}"
+            if [[ $extension == 'py' ]]; then
+              changed_files_pylint+=" ${files}"
+            fi
+          done
+
+          if [[ ! -z ${changed_files_pylint} ]]; then
+            sudo apt-get --no-install-recommends install -y build-essential curl python3-dev python3-pip python3-venv
+            python3 -m venv .env
+            . .env/bin/activate
+            pip install -U pip wheel setuptools
+            pip install pylint-json2html
+            pip install $(egrep "pylint.*" ./cvat/requirements/development.txt)
+            mkdir -p pylint_report
+
+            echo "Pylint version: "`pylint --version | head -1`
+            echo "The files will be checked: "`echo ${changed_files_pylint}`
+            pylint ${changed_files_pylint} --output-format=json > ./pylint_report/pylint_checks.json || exit_code=`echo $?` || true
+            pylint-json2html -o ./pylint_report/pylint_checks.html ./pylint_report/pylint_checks.json
+            deactivate
+            exit ${exit_code}
+          else
+            echo "No files with the \"py\" extension found"
+          fi
+
+      - name: Upload artifacts
+        if: failure()
+        uses: actions/upload-artifact@v2
+        with:
+          name: pylint_report
+          path: pylint_report