add workflow to publish to PyPI

This workflow is triggered when publishing a new release
using the GitHub Releases functionality. It can also be
triggered manually for testing.

The workflow will always publish to Test PyPI, but will
only publish to the real PyPI, when releasing a new
version using the GitHub Releases functionality.

The version for the package is generated by setuptools_scm,
based on the git tags/commits. For all non-tagged commits,
a "dev version" is generated with the format "0.1.2-dev3",
where 0.1.2 is the latest tag plus one more in the last part
of the version number (i.e. given the last tag was 0.1.1,
0.1.2 will be used for the dev version) and the 3 in "-dev3"
comes from the number of commits since the last tag.
(This all is standard setuptools_scm behaviour.)

Author: wnienhaus

.github/workflows/publish.yml

@@ -0,0 +1,42 @@
+name: Publish Python Package
+
+on:
+  # trigger when publishing a release
+  release:
+    types: [published]
+
+  # also allow triggering this workflow manually for testing
+  workflow_dispatch:
+
+jobs:
+  publish:
+
+    runs-on: ubuntu-latest
+
+    steps:
+    - name: Checkout
+      uses: actions/checkout@v2
+      with:
+        # just fetching 1 commit is not enough for setuptools-scm, so we fetch all
+        fetch-depth: 0
+    - name: Set up Python
+      uses: actions/setup-python@v2
+      with:
+        python-version: '3.x'
+    - name: Install dependencies
+      run: |
+        pip install setuptools setuptools_scm
+    - name: Build package
+      run: |
+        python setup.py sdist
+        rm dist/*.orig  # clean sdist_upip noise
+    - name: Publish to Test PyPI
+      uses: pypa/gh-action-pypi-publish@release/v1
+      with:
+        password: ${{ secrets.TEST_PYPI_API_TOKEN }}
+        repository_url: https://test.pypi.org/legacy/
+    - name: Publish to PyPI
+      uses: pypa/gh-action-pypi-publish@release/v1
+      if: github.event.release.tag_name  # only when releasing a new version
+      with:
+        password: ${{ secrets.PYPI_API_TOKEN }}