Update workflow

.github/workflows/check_changelog.yaml

@@ -1,33 +1,35 @@
 name: Verify changelog updated
 
 on: 
-  push:
-    paths:
-      - '**.rst'
-      - '**.py'
   pull_request:
     paths:
       - '**.rst'
       - '**.py'
+    types:
+      - opened
+      - ready_for_review
 
 
 jobs:
-  check:
+  check_changes:
     runs-on: ubuntu-latest
-
     steps:
-    - name: Checkout Code
-      uses: actions/checkout@v2
-      with:
-        fetch-depth: 0
+      - name: Checkout repo
+        uses: actions/checkout@v2
 
-    - name: Check for Change Log Modification
-      run: |
-        changelog_modified=$(echo "$changed_files" | grep '^CHANGELOG.rst$' || true)
-        if [ -z "$changelog_modified" ] && [ ! -z "$python_or_rst_modified" ]
-        then
-          echo "Error: Changelog not modified while .rst or .py files have been modified"
-          exit 1
-        else
-          echo "Changelog modified or no .rst/.py files have been modified"
-        fi
+      - name: Get changed files
+        id: getfile
+        run: |
+          echo "Files changed:"
+          CHANGED_FILES=$(git diff --name-only ${{ github.event.pull_request.base.sha }} ${{ github.event.pull_request.head.sha }})
+          echo "$CHANGED_FILES"
+          echo "CHANGED_FILES<<EOF" >> $GITHUB_ENV
+          echo "$CHANGED_FILES" >> $GITHUB_ENV
+          echo "EOF" >> $GITHUB_ENV
+          
+      - name: Comment PR
+        uses: thollander/actions-comment-pull-request@master
+        with:
+           message: 'Thank you for the PR! The changelog has not been updated so here is a friendly reminder to check if you need at add an entry.'
+           GITHUB_TOKEN: '${{ secrets.GITHUB_TOKEN }}'
+        if: contains(fromJson(env.CHANGED_FILES), '.py') && !contains(fromJson(env.CHANGED_FILES), 'changelog.rst')