Support for specifying a minimum supported Python version

CHANGES.rst

@@ -4,6 +4,9 @@ Change log
 1.1 (unreleased)
 ----------------
 
+- Allow specifying a minimum supported Python version other than the previously
+  hardcoded default of Python 3.8.
+
 
 1.0 (2024-10-02)
 ----------------

docs/narr.rst

@@ -176,6 +176,11 @@ The following options are only needed one time as their values are stored in
   a final release thus it is not yet generally supported by the zopefoundation
   packages.
 
+--oldest-python
+  The oldest version of Python supported by this package. Specified as version
+  number, e.g. ``3.8``. This setting is optional and defaults to the lowest
+  Python version generally supported by zopefoundation packages.
+
 --with-docs
   Enable building the documentation using Sphinx. This will also create a
   configuration file `.readthedocs.yaml` for integration with

src/zope/meta/config_package.py

@@ -19,6 +19,8 @@
 
 import jinja2
 import tomlkit
+from packaging.version import InvalidVersion
+from packaging.version import parse as parse_version
 
 from .set_branch_protection_rules import set_branch_protection
 from .shared.call import abort
@@ -105,6 +107,12 @@ def handle_command_line_arguments():
         default=False,
         help='Activate support for a future non-final Python version if not'
         ' already configured in .meta.toml.')
+    parser.add_argument(
+        '--oldest-python',
+        dest='oldest_python',
+        default=OLDEST_PYTHON_VERSION,
+        help='Oldest supported Python version. Defaults to'
+             f'Python {OLDEST_PYTHON_VERSION}.')
     parser.add_argument(
         '--with-docs',
         # people (me) use --with-sphinx and accidentally
@@ -197,6 +205,21 @@ def config_type(self):
                 'Please use `--type` to select it.')
         return value
 
+    @cached_property
+    def oldest_python(self):
+        value = (self.meta_cfg['python'].get('oldest-python') or
+                 self.args.oldest_python)
+        try:
+            version = parse_version(value)
+        except InvalidVersion:
+            raise ValueError(f'Invalid value {value} for oldest Python.')
+
+        if version > parse_version(NEWEST_PYTHON_VERSION):
+            raise ValueError('Oldest Python version cannot be higher than'
+                             ' newest supported Python')
+
+        return value
+
     @cached_property
     def config_type_path(self):
         return pathlib.Path(__file__).parent / self.config_type
@@ -348,7 +371,7 @@ def pre_commit_config_yaml(self):
             "pre-commit-config.yaml.j2",
             self.path / ".pre-commit-config.yaml",
             self.config_type,
-            oldest_python_version=OLDEST_PYTHON_VERSION.replace(".", ""),
+            oldest_python_version=self.oldest_python.replace(".", ""),
             teyit_exclude=teyit_exclude,
         )
 
@@ -391,7 +414,7 @@ def manylinux_sh(self):
                 with_future_python=self.with_future_python,
                 future_python_shortversion=FUTURE_PYTHON_SHORTVERSION,
                 supported_python_versions=supported_python_versions(
-                    short_version=True),
+                    self.oldest_python, short_version=True),
                 stop_at=stop_at,
             )
             (self.path / '.manylinux-install.sh').chmod(0o755)
@@ -477,7 +500,7 @@ def tox(self):
             setuptools_version_spec=SETUPTOOLS_VERSION_SPEC,
             future_python_shortversion=FUTURE_PYTHON_SHORTVERSION,
             supported_python_versions=supported_python_versions(
-                short_version=True),
+                self.oldest_python, short_version=True),
         )
 
     def tests_yml(self):
@@ -496,8 +519,10 @@ def tests_yml(self):
         require_cffi = self.meta_cfg.get(
             'c-code', {}).get('require-cffi', False)
         py_version_matrix = [
-            x for x in zip(supported_python_versions(short_version=False),
-                           supported_python_versions(short_version=True))]
+            x for x in zip(supported_python_versions(self.oldest_python,
+                                                     short_version=False),
+                           supported_python_versions(self.oldest_python,
+                                                     short_version=True))]
         self.copy_with_meta(
             'tests.yml.j2',
             workflows / 'tests.yml',

src/zope/meta/set_branch_protection_rules.py

@@ -23,7 +23,6 @@
 
 
 BASE_URL = f'https://raw.githubusercontent.com/{ORG}'
-OLDEST_PYTHON = f'py{OLDEST_PYTHON_VERSION.replace(".", "")}'
 NEWEST_PYTHON = f'py{NEWEST_PYTHON_VERSION.replace(".", "")}'
 DEFAULT_BRANCH = 'master'
 
@@ -71,6 +70,9 @@ def set_branch_protection(
     template = meta_toml['meta']['template']
     with_docs = meta_toml['python'].get('with-docs', False)
     with_pypy = meta_toml['python']['with-pypy']
+    oldest_python_version = meta_toml['python'].get('oldest-python',
+                                                    OLDEST_PYTHON_VERSION)
+    oldest_python = oldest_python_version.replace('.', '')
     with_windows = meta_toml['python']['with-windows']
     with_macos = meta_toml['python']['with-macos']
     required = ['linting']
@@ -79,9 +81,9 @@ def set_branch_protection(
             f'manylinux ({MANYLINUX_PYTHON_VERSION}, {MANYLINUX_AARCH64})',
             f'manylinux ({MANYLINUX_PYTHON_VERSION}, {MANYLINUX_I686})',
             f'manylinux ({MANYLINUX_PYTHON_VERSION}, {MANYLINUX_X86_64})',
-            f'test ({OLDEST_PYTHON_VERSION}, macos-latest)',
+            f'test ({oldest_python_version}, macos-latest)',
             f'test ({NEWEST_PYTHON_VERSION}, macos-latest)',
-            f'test ({OLDEST_PYTHON_VERSION}, ubuntu-latest)',
+            f'test ({oldest_python_version}, ubuntu-latest)',
             f'test ({NEWEST_PYTHON_VERSION}, ubuntu-latest)',
             'coveralls_finish',
         ])
@@ -93,23 +95,23 @@ def set_branch_protection(
             required.append(f'test (pypy-{PYPY_VERSION}, windows-latest)')
         if with_windows:
             required.extend([
-                f'test ({OLDEST_PYTHON_VERSION}, windows-latest)',
+                f'test ({oldest_python_version}, windows-latest)',
                 f'test ({NEWEST_PYTHON_VERSION}, windows-latest)',
             ])
     elif with_windows or with_macos:
         required.extend([
             'ubuntu-coverage',
-            f'ubuntu-{OLDEST_PYTHON}',
+            f'ubuntu-{oldest_python}',
             f'ubuntu-{NEWEST_PYTHON}',
         ])
         if with_windows:
             required.extend([
-                f'windows-{OLDEST_PYTHON}',
+                f'windows-{oldest_python}',
                 f'windows-{NEWEST_PYTHON}',
             ])
         if with_macos:
             required.extend([
-                f'macos-{OLDEST_PYTHON}',
+                f'macos-{oldest_python}',
                 f'macos-{NEWEST_PYTHON}',
             ])
         if with_pypy:
@@ -120,7 +122,7 @@ def set_branch_protection(
         if with_docs:
             required.append('ubuntu-docs')
     else:  # default for most packages
-        required.extend([OLDEST_PYTHON, NEWEST_PYTHON])
+        required.extend([oldest_python, NEWEST_PYTHON])
         if template != 'toolkit':
             required.append('coverage')
         if with_docs:

src/zope/meta/shared/packages.py

@@ -145,20 +145,23 @@ def parse_additional_config(cfg):
     return data
 
 
-def supported_python_versions(short_version=False):
+def supported_python_versions(oldest_version=OLDEST_PYTHON_VERSION,
+                              short_version=False):
     """Create a list containing all supported Python versions
 
     Uses the configured oldest and newest Python versions to compute a list
     containing all versions from oldest to newest that can be iterated over in
     the templates.
 
     Kwargs:
+        oldest_version (str):
+            The oldest supported Python version, e.g. '3.8'.
 
         short_version (bool):
-            Return short versions like "313" instead of "3.13"
+            Return short versions like "313" instead of "3.13". Default False.
     """
     minor_versions = []
-    oldest_python = parse_version(OLDEST_PYTHON_VERSION)
+    oldest_python = parse_version(oldest_version)
     newest_python = parse_version(NEWEST_PYTHON_VERSION)
     for minor in range(oldest_python.minor, newest_python.minor + 1):
         minor_versions.append(minor)

src/zope/meta/update_python_support.py

@@ -84,14 +84,20 @@ def main():
         with open('.meta.toml', 'rb') as meta_f:
             meta_toml = collections.defaultdict(dict, **tomlkit.load(meta_f))
         config_type = meta_toml['meta']['template']
+        oldest_python_version = meta_toml['python'].get('oldest-python',
+                                                        OLDEST_PYTHON_VERSION)
         branch_name = get_branch_name(args.branch_name, config_type)
         updating = git_branch(branch_name)
 
         current_python_versions = get_tox_ini_python_versions('tox.ini')
-        no_longer_supported = (set(current_python_versions) -
-                               set(supported_python_versions()))
-        not_yet_supported = (set(supported_python_versions()) -
-                             set(current_python_versions))
+        no_longer_supported = (
+            set(current_python_versions) -
+            set(supported_python_versions(oldest_python_version))
+        )
+        not_yet_supported = (
+            set(supported_python_versions(oldest_python_version)) -
+            set(current_python_versions)
+        )
 
         non_interactive_params = []
         python_versions_args = []
@@ -107,21 +113,23 @@ def main():
             sys.exit(0)
 
         if no_longer_supported:
-            for version in sorted(list(no_longer_supported)):
-                call(bin_dir / 'addchangelogentry',
-                     f'Drop support for Python {version}.',
-                     *non_interactive_params)
+            version_spec = ', '.join(sorted(no_longer_supported))
+            call(bin_dir / 'addchangelogentry',
+                 f'Drop support for Python {version_spec}.',
+                 *non_interactive_params)
             python_versions_args.append(
                 '--drop=' + ','.join(no_longer_supported))
 
         if not_yet_supported:
-            for version in sorted(list(not_yet_supported)):
-                call(
-                    bin_dir / 'addchangelogentry',
-                    f'Add support for Python {version}.',
-                    *non_interactive_params)
-            python_versions_args = ['--add=' +
-                                    ','.join(supported_python_versions())]
+            version_spec = ', '.join(sorted(not_yet_supported))
+            call(
+                bin_dir / 'addchangelogentry',
+                f'Add support for Python {version_spec}.',
+                *non_interactive_params)
+            python_versions_args = [
+                '--add=' +
+                ','.join(supported_python_versions(oldest_python_version))
+            ]
 
         if no_longer_supported or not_yet_supported:
             call(bin_dir / 'check-python-versions', '--only=setup.py',
@@ -130,8 +138,7 @@ def main():
             call(os.environ['EDITOR'], '.meta.toml')
 
             config_package_args = [
-                sys.executable,
-                'config-package.py',
+                bin_dir / 'config-package',
                 path,
                 f'--branch={branch_name}',
                 '--no-push',
@@ -140,7 +147,7 @@ def main():
                 config_package_args.append('--no-commit')
             call(*config_package_args, cwd=cwd_str)
             src = path.resolve() / 'src'
-            py_ver_plus = f'--py{OLDEST_PYTHON_VERSION.replace(".", "")}-plus'
+            py_ver_plus = f'--py{oldest_python_version.replace(".", "")}-plus'
             call('find', src, '-name', '*.py', '-exec', bin_dir / 'pyupgrade',
                  '--py3-plus', py_ver_plus, '{}', ';')
             call(bin_dir / 'pyupgrade',