improv: CI to run on pull requests

instruct GitHub Actions to run upon pull requests according to the docs

.github/workflows/pythonpackage.yml

@@ -1,34 +1,42 @@
-name: Python package
+name: Powertools Python
 
 on:
+  pull_request:
+    branches:
+      - develop
+      - master
+    paths:
+      - "python/**"
   push:
+    branches:
+      - develop
+      - master
     paths:
-    - 'python/**'
+      - "python/**"
 
 jobs:
   build:
-
     runs-on: ubuntu-latest
     strategy:
       max-parallel: 4
       matrix:
         python-version: [3.6, 3.7]
     steps:
-    - uses: actions/checkout@v1
-    - name: Set up Python ${{ matrix.python-version }}
-      uses: actions/setup-python@v1
-      with:
-        python-version: ${{ matrix.python-version }}
-    - name: Install dependencies
-      run: |
-        python -m pip install --upgrade pip
-        make dev
-      working-directory: ./python/
-    - name: Formatting and Linting
-      run: |
-        make lint
-      working-directory: ./python/
-    - name: Test with pytest
-      run: |
-        make test
-      working-directory: ./python/
+      - uses: actions/checkout@v1
+      - name: Set up Python ${{ matrix.python-version }}
+        uses: actions/setup-python@v1
+        with:
+          python-version: ${{ matrix.python-version }}
+      - name: Install dependencies
+        run: |
+          python -m pip install --upgrade pip
+          make dev
+        working-directory: ./python/
+      - name: Formatting and Linting
+        run: |
+          make lint
+        working-directory: ./python/
+      - name: Test with pytest
+        run: |
+          make test
+        working-directory: ./python/

python/Makefile

@@ -3,6 +3,7 @@ target:
 	@$(MAKE) pr
 
 dev:
+	pip install --upgrade pipenv
 	pipenv install
 	pipenv install -d