feat: support Python 3.9 and 3.10

Lower the minimum supported Python from 3.11 to 3.9 to cover stock macOS
and Debian/Ubuntu interpreters.

- Fall back to the tomli backport when tomllib is unavailable (< 3.11),
  in both the manifest loader and the solution-coverage test.
- Add 'from __future__ import annotations' to exercise.py so the
  'Path | None' dataclass fields are not evaluated at class-definition
  time on < 3.10.
- type_hints4 / type_hints8 teach PEP 604 'int | None' unions: add the
  future import to the exercise scaffold and reference answer, and assert
  on the textual annotation in the checks so they pass on 3.9-3.13.
- itertools8 teaches itertools.pairwise (3.10+): provide the documented
  tee-based fallback in the scaffold and answer; the learner's task is
  unchanged.
- Bump version to 0.2.0, add 3.9/3.10 classifiers, and declare the
  conditional tomli dependency.

Author: abhiksark

CHANGELOG.md

@@ -3,6 +3,26 @@
 All notable changes to this project are documented here. Pylings follows
 Semantic Versioning.
 
+## [0.2.0] - 2026-05-30
+
+### Added
+
+- Support for Python 3.9 and 3.10 (minimum was 3.11), broadening
+  compatibility with stock macOS and Debian/Ubuntu interpreters.
+
+### Changed
+
+- The `type_hints4`, `type_hints8`, and `itertools8` exercises carry a small
+  forward-compatibility shim (`from __future__ import annotations` and a
+  `tee`-based `pairwise` fallback) so their modern syntax and stdlib usage run
+  on Python 3.9 and 3.10. The learner's task is unchanged.
+
+### Fixed
+
+- Manifest loading now falls back to the `tomli` backport on Python < 3.11,
+  where `tomllib` is not available in the standard library. Previously the
+  package would install but crash on launch under older interpreters.
+
 ## [0.1.0] - 2026-05-25
 
 ### Added

checks/type_hints/type_hints4.py

@@ -1,9 +1,5 @@
-import types
-
 hints = find_index.__annotations__
-assert hints.get("items") == list[str], "items should be annotated as list[str]"
-assert hints.get("target") is str, "target should be annotated as str"
-ret = hints.get("return")
-assert isinstance(ret, types.UnionType) and ret == (int | None), \
-    "return type should be int | None"
+assert hints.get("items") == "list[str]", "items should be annotated as list[str]"
+assert hints.get("target") == "str", "target should be annotated as str"
+assert hints.get("return") == "int | None", "return type should be int | None"
 print("type_hints4 ✓")

checks/type_hints/type_hints8.py

@@ -1,13 +1,9 @@
-import types
-
 hints = summarise.__annotations__
-assert hints.get("records") == list[dict[str, int]], \
+assert hints.get("records") == "list[dict[str, int]]", \
     "records should be annotated as list[dict[str, int]]"
-assert hints.get("key") is str, "key should be annotated as str"
-default_hint = hints.get("default")
-assert isinstance(default_hint, types.UnionType) and default_hint == (int | None), \
+assert hints.get("key") == "str", "key should be annotated as str"
+assert hints.get("default") == "int | None", \
     "default should be annotated as int | None"
-ret = hints.get("return")
-assert ret == dict[str, int | None], \
+assert hints.get("return") == "dict[str, int | None]", \
     "return type should be dict[str, int | None]"
 print("type_hints8 ✓")

exercises/itertools/itertools8.py

@@ -3,7 +3,15 @@
 #
 # Goal: Flatten batches, then collect every pair of adjacent flattened values.
 
-from itertools import pairwise
+try:
+    from itertools import pairwise
+except ImportError:  # Python < 3.10
+    from itertools import tee
+
+    def pairwise(iterable):
+        a, b = tee(iterable)
+        next(b, None)
+        return zip(a, b)
 
 batches = [[1, 2], [3], [4, 5]]
 flattened = [item for batch in batches for item in batch]

exercises/type_hints/type_hints4.py

@@ -8,6 +8,11 @@
 #
 # The signature should read:
 #   def find_index(items: list[str], target: str) -> int | None:
+#
+# Keep the `from __future__ import annotations` line below: it lets the modern
+# `int | None` syntax work on Python 3.9 and 3.10 as well.
+from __future__ import annotations
+
 
 def find_index(items, target):
     try:

exercises/type_hints/type_hints8.py

@@ -13,6 +13,11 @@
 #       key: str,
 #       default: int | None,
 #   ) -> dict[str, int | None]:
+#
+# Keep the `from __future__ import annotations` line below: it lets the modern
+# `int | None` syntax work on Python 3.9 and 3.10 as well.
+from __future__ import annotations
+
 
 def summarise(records, key, default):
     return {

pylings/cli.py

@@ -5,7 +5,7 @@
 import sys
 from pathlib import Path
 
-__version__ = "0.1.0"
+__version__ = "0.2.0"
 
 
 def _build_parser() -> argparse.ArgumentParser:

pylings/core/exercise.py

@@ -1,4 +1,5 @@
 # pylings/core/exercise.py
+from __future__ import annotations
 
 from dataclasses import dataclass
 from pathlib import Path

pylings/core/manifest.py

@@ -1,7 +1,10 @@
 # pylings/core/manifest.py
 from __future__ import annotations
 
-import tomllib
+try:
+    import tomllib
+except ModuleNotFoundError:  # Python < 3.11
+    import tomli as tomllib
 from dataclasses import dataclass
 from pathlib import Path
 

pyproject.toml

@@ -4,10 +4,10 @@ build-backend = "hatchling.build"
 
 [project]
 name = "python-learnings"
-version = "0.1.0"
+version = "0.2.0"
 description = "Python learnings, Rustlings-style, in a terminal TUI."
 readme = "Readme.md"
-requires-python = ">=3.11"
+requires-python = ">=3.9"
 license = { text = "MIT" }
 keywords = [
     "python",
@@ -30,6 +30,8 @@ classifiers = [
     "License :: OSI Approved :: MIT License",
     "Operating System :: OS Independent",
     "Programming Language :: Python :: 3",
+    "Programming Language :: Python :: 3.9",
+    "Programming Language :: Python :: 3.10",
     "Programming Language :: Python :: 3.11",
     "Programming Language :: Python :: 3.12",
     "Programming Language :: Python :: 3.13",
@@ -40,6 +42,7 @@ classifiers = [
 dependencies = [
     "textual[syntax]>=8.0.0",
     "watchdog>=6.0.0",
+    "tomli>=1.1.0; python_version < '3.11'",
 ]
 
 [project.urls]