Support lower Python versions >=3.9 (#720)

Co-authored-by: konstantin <konstantin.klein@hochfrequenz.de>

Author: hf-krechan

.github/workflows/packaging_test.yml

@@ -6,7 +6,7 @@ jobs:
     runs-on: ${{ matrix.os }}
     strategy:
       matrix:
-        python-version: ["3.11"]
+        python-version: ["3.9", "3.10", "3.11", "3.12"]
         os: [ubuntu-latest]
     steps:
       - uses: actions/checkout@v4

.github/workflows/python-publish-scheduled.yml

@@ -13,7 +13,7 @@ jobs:
     runs-on: ${{ matrix.os }}
     strategy:
       matrix:
-        python-version: ["3.11"]
+        python-version: ["3.9", "3.10", "3.11", "3.12"]
         os: [ubuntu-latest]
     steps:
       - uses: actions/checkout@v4

.github/workflows/tests.yml

@@ -6,7 +6,7 @@ jobs:
     runs-on: ${{ matrix.os }}
     strategy:
       matrix:
-        python-version: ["3.10", "3.11", "3.12"]
+        python-version: ["3.9", "3.10", "3.11", "3.12"]
         os: [ubuntu-latest]
     steps:
       - uses: actions/checkout@v4

pyproject.toml

@@ -6,7 +6,7 @@ build-backend = "hatchling.build"
 name = "bo4e"
 description = "Python Library that implements the BO4E Standard."
 license = { text = "MIT" }
-requires-python = ">=3.10"
+requires-python = ">=3.9"
 authors = [
   { name = "Kevin Krechan", email = "kevin.krechan@hochfrequenz.de" },
   { name = "Leon Haffmans", email = "leon.haffmans@hochfrequenz.de" },
@@ -22,6 +22,7 @@ classifiers = [
   "Operating System :: OS Independent",
   "Programming Language :: Python",
   "Programming Language :: Python :: 3 :: Only",
+  "Programming Language :: Python :: 3.9",
   "Programming Language :: Python :: 3.10",
   "Programming Language :: Python :: 3.11",
   "Programming Language :: Python :: 3.12",

tests/serialization_helper.py

@@ -2,6 +2,8 @@
 A module that simplifies assertions for json serialization
 """
 
+from __future__ import annotations
+
 from typing import Any, Dict, Optional, TypeVar
 
 from dictdiffer import diff  # type:ignore[import-not-found]

tests/test_zusatz_attribut.py

@@ -1,3 +1,5 @@
+from __future__ import annotations
+
 import pytest
 
 from bo4e import Anrede, Organisationstyp, Titel