Added a GitHub Action that will run flake8 on submitted PRs (#651)

* Added new Python linter (flake8). It will run as a GitHub Action on every pull request. It will annotate every error it finds.

* Update flake8_python_linter.yml

* Update flake8_python_linter.yml

* Update flake8_python_linter.yml

* Update flake8_python_linter.yml

Added more errors/warnings to ignore.

* Updated requirements.txt by adding flake8

.github/workflows/flake8_python_linter.yml

@@ -0,0 +1,40 @@
+# This workflow runs flake8 with reviewdog. The documentation can be found below:
+# https://github.com/marketplace/actions/run-flake8-with-reviewdog
+# Flake8 is a Python linter that analyzes code and checks for programming and stylistic errors
+name: Flake8 Linter
+
+# This workflow acts only on pull requests
+on: pull_request
+
+jobs:
+
+  flake8-lint:
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Check out source repository
+        uses: actions/checkout@v2
+
+      - name: Set up Python environment
+        uses: actions/setup-python@v2
+        with:
+          python-version: "3.8"
+
+      - name: Flake8 Lint
+        uses: reviewdog/action-flake8@v3
+        with:
+          # For more flake 8 arguments, visit the link below:
+          # https://flake8.pycqa.org/en/latest/user/options.html
+          # Currently, flake8 ignores the following;
+          #     W291: Trailing whitespace
+          #     W292: No newline at end of file
+          #     W293: Blank line contains whitespace
+          #     E202: Whitespace before ')'
+          #     E203: Whitespace before ':'
+          #     E221: Multiple spaces before operator
+          #     E241: Multiple spaces after ','
+          #     E251: Unexpected spaces around keyword / parameter equals
+          #     E272: Multiple spaces before keyword
+          flake8_args: "--ignore=W291,W292,W293,E202,E203,E221,E241,E251,E272 --max-line-length 120"
+          github_token: ${{ secrets.GITHUB_TOKEN }}
+

python/requirements.txt

@@ -15,3 +15,4 @@ python-dateutil
 nibabel
 numpy
 scipy
+flake8