add flake8 python version check script and CI check

.github/workflows/flake8_py_version_check.yml

@@ -0,0 +1,13 @@
+name: flake8_py_version_check
+on:
+  workflow_dispatch: {}
+  schedule:
+  # every Sunday at midnight
+  - cron: "0 0 * * 0"
+jobs:
+  check-versions:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v4
+    - name: run script
+      run: python scripts/flake8_py_version_check.py

scripts/flake8_py_version_check.py

@@ -0,0 +1,36 @@
+import json
+import re
+import subprocess
+
+
+def main():
+    # find a line in pyproject.toml that looks like `python-requires = "..."`
+    # with forgiving spacing and single or double quotes
+    with open("pyproject.toml") as fp:
+        pyproject_txt = fp.read()
+    match = re.search(r"""\n\s*requires-python\s*=\s*['"](.*)['"]""", pyproject_txt)
+    assert match is not None, "'requires-python' line not found in pyproject.toml"
+
+    flake8_bugbear_requires = match.group(1).strip()
+
+    # get pypi data for flake8 as json
+    curl_output = subprocess.getoutput(
+        "curl -L -s --header 'Accept: application/vnd.pypi.simple.v1+json'"
+        " https://pypi.org/simple/flake8"
+    )
+    flake8_pypi_data = json.loads(curl_output)
+
+    # find latest non-yanked flake8 file data
+    latest_file_data = next(
+        file for file in reversed(flake8_pypi_data["files"]) if not file["yanked"]
+    )
+    flake8_requires = latest_file_data["requires-python"]
+
+    assert flake8_requires == flake8_bugbear_requires, (
+        f"python version requirements don't match: ({flake8_requires=} !="
+        f" {flake8_bugbear_requires=})"
+    )
+
+
+if __name__ == "__main__":
+    main()