Split python into separate script

CHANGELOG.md

@@ -11,6 +11,7 @@ This project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.htm
 
 ## Changed
 - "Dogfood" action to check itself
+- Move python code out of workflow file
 
 ## [v1.0.0] - 2024-04-18
 

action.yml

@@ -15,36 +15,21 @@ runs:
     - name: Checkout repository
       uses: actions/checkout@v4
 
+    - uses: actions/setup-python@v5
+      with:
+        python-version: '3.10'
+
     # https://github.com/orgs/community/discussions/9049#discussioncomment-4239509
     # Due to limitations on composite Actions, we can't do something like:
     # - uses: docker://ghcr.io/uclahs-cds/cicd-base:${{ inputs.docker-tag }}
     # Instead, we need to write another action.yml on-the-fly and then use that.
     # There absolutely should not be an 'action.yml' file underneath the .git
     # folder of the calling repository already, so we can use that.
     - name: Configure workflow
-      shell: python
       env:
         DOCKER_IMAGE_TAG: ${{ inputs.docker-tag }}
-      run: |
-          import os
-          import re
-          from pathlib import Path
-
-          # Bail out if there are any illegal characters in the tag
-          tag = os.environ.get("DOCKER_IMAGE_TAG")
-          if re.search(r"[^a-zA-Z0-9_.\-]", tag):
-              raise ValueError(f"Problem with the tag `{tag}`!")
-
-          template = Path(
-              os.environ.get("GITHUB_ACTION_PATH"), "template", "action.yml"
-          )
-
-          Path(".git/action.yml").write_text(
-              template.read_text(encoding="utf-8").replace(
-                  "DOCKER_IMAGE_TAG", tag
-              ),
-              encoding="utf-8"
-          )
+      shell: bash
+      run: python '${{ github.action_path }}/create_template.py'
 
     - name: Run checks
       uses: ./.git

create_template.py

@@ -0,0 +1,20 @@
+#!/usr/bin/env python3
+"Generate an action.yml file from the template."
+import os
+import re
+from pathlib import Path
+
+# Bail out if there are any illegal characters in the tag
+tag = os.environ.get("DOCKER_IMAGE_TAG")
+if re.search(r"[^a-zA-Z0-9_.\-]", tag):
+    raise ValueError(f"Problem with the tag `{tag}`!")
+
+template = Path(os.environ.get("GITHUB_ACTION_PATH"), "template", "action.yml")
+output_file = Path(os.environ.get("GITHUB_WORKSPACE"), ".git", "action.yml")
+
+output_file.write_text(
+    template.read_text(encoding="utf-8").replace(
+        "DOCKER_IMAGE_TAG", tag
+    ),
+    encoding="utf-8"
+)