Drop Python 3.8 support

This addresses a failure in the `py38-dev` tests
caused by markupsafe recently dropping Python 3.8 support.

Changed in this commit:

* Drop Python 3.8 support
* Update CI and tox testing
* Update docs references to Python 3.8
* Remove a Windows / Python 3.8 admonition in the docs
* Address type annotations
* Incorporate style fixes

Still to do:

* `src/flask/sessions.py` contains these comments:

  > TODO generic when Python > 3.8

  This TODO should now be unblocked.

.github/workflows/tests.yaml

@@ -28,10 +28,9 @@ jobs:
           - {python: '3.11'}
           - {python: '3.10'}
           - {python: '3.9'}
-          - {python: '3.8'}
           - {name: PyPy, python: 'pypy-3.10', tox: pypy310}
           - {name: Minimum Versions, python: '3.12', tox: py-min}
-          - {name: Development Versions, python: '3.8', tox: py-dev}
+          - {name: Development Versions, python: '3.9', tox: py-dev}
     steps:
       - uses: actions/checkout@eef61447b9ff4aafe5dcd4e0bbf5d482be7e7871 # v4.2.1
       - uses: actions/setup-python@f677139bbe7f9c59b41e40162b753c062f5d49a3 # v5.2.0

docs/async-await.rst

@@ -23,12 +23,6 @@ method in views that inherit from the :class:`flask.views.View` class, as
 well as all the HTTP method handlers in views that inherit from the
 :class:`flask.views.MethodView` class.
 
-.. admonition:: Using ``async`` on Windows on Python 3.8
-
-    Python 3.8 has a bug related to asyncio on Windows. If you encounter
-    something like ``ValueError: set_wakeup_fd only works in main thread``,
-    please upgrade to Python 3.9.
-
 .. admonition:: Using ``async`` with greenlet
 
     When using gevent or eventlet to serve an application or patch the

docs/extensiondev.rst

@@ -294,7 +294,7 @@ ecosystem remain consistent and compatible.
     indicate minimum compatibility support. For example,
     ``sqlalchemy>=1.4``.
 9.  Indicate the versions of Python supported using ``python_requires=">=version"``.
-    Flask itself supports Python >=3.8 as of April 2023, but this will update over time.
+    Flask itself supports Python >=3.9 as of October 2024, but this will update over time.
 
 .. _PyPI: https://pypi.org/search/?c=Framework+%3A%3A+Flask
 .. _Discord Chat: https://discord.gg/pallets

docs/installation.rst

@@ -5,7 +5,7 @@ Installation
 Python Version
 --------------
 
-We recommend using the latest version of Python. Flask supports Python 3.8 and newer.
+We recommend using the latest version of Python. Flask supports Python 3.9 and newer.
 
 
 Dependencies

examples/celery/pyproject.toml

@@ -3,7 +3,7 @@ name = "flask-example-celery"
 version = "1.0.0"
 description = "Example Flask application with Celery background tasks."
 readme = "README.md"
-requires-python = ">=3.8"
+requires-python = ">=3.9"
 dependencies = ["flask>=2.2.2", "celery[redis]>=5.2.7"]
 
 [build-system]

pyproject.toml

@@ -19,7 +19,7 @@ classifiers = [
     "Topic :: Software Development :: Libraries :: Application Frameworks",
     "Typing :: Typed",
 ]
-requires-python = ">=3.8"
+requires-python = ">=3.9"
 dependencies = [
     "Werkzeug>=3.0.0",
     "Jinja2>=3.1.2",
@@ -78,7 +78,7 @@ source = ["flask", "tests"]
 source = ["src", "*/site-packages"]
 
 [tool.mypy]
-python_version = "3.8"
+python_version = "3.9"
 files = ["src/flask", "tests/typing"]
 show_error_codes = true
 pretty = true
@@ -94,7 +94,7 @@ module = [
 ignore_missing_imports = true
 
 [tool.pyright]
-pythonVersion = "3.8"
+pythonVersion = "3.9"
 include = ["src/flask", "tests"]
 typeCheckingMode = "basic"
 

src/flask/helpers.py

@@ -5,7 +5,7 @@ import os
 import sys
 import typing as t
 from datetime import datetime
-from functools import lru_cache
+from functools import cache
 from functools import update_wrapper
 
 import werkzeug.utils
@@ -623,7 +623,7 @@ def get_root_path(import_name: str) -> str:
     return os.path.dirname(os.path.abspath(filepath))  # type: ignore[no-any-return]
 
 
-@lru_cache(maxsize=None)
+@cache
 def _split_blueprint_path(name: str) -> list[str]:
     out: list[str] = [name]
 

src/flask/typing.py

@@ -12,7 +12,7 @@ ResponseValue = t.Union[
     "Response",
     str,
     bytes,
-    t.List[t.Any],
+    list[t.Any],
     # Only dict is actually accepted, but Mapping allows for TypedDict.
     t.Mapping[str, t.Any],
     t.Iterator[str],
@@ -21,21 +21,21 @@ ResponseValue = t.Union[
 
 # the possible types for an individual HTTP header
 # This should be a Union, but mypy doesn't pass unless it's a TypeVar.
-HeaderValue = t.Union[str, t.List[str], t.Tuple[str, ...]]
+HeaderValue = t.Union[str, list[str], tuple[str, ...]]
 
 # the possible types for HTTP headers
 HeadersValue = t.Union[
     "Headers",
     t.Mapping[str, HeaderValue],
-    t.Sequence[t.Tuple[str, HeaderValue]],
+    t.Sequence[tuple[str, HeaderValue]],
 ]
 
 # The possible types returned by a route function.
 ResponseReturnValue = t.Union[
     ResponseValue,
-    t.Tuple[ResponseValue, HeadersValue],
+    tuple[ResponseValue, HeadersValue],
-    t.Tuple[ResponseValue, int],
+    tuple[ResponseValue, int],
-    t.Tuple[ResponseValue, int, HeadersValue],
+    tuple[ResponseValue, int, HeadersValue],
     "WSGIApplication",
 ]
 
@@ -56,21 +56,21 @@ BeforeRequestCallable = t.Union[
     t.Callable[[], t.Optional[ResponseReturnValue]],
     t.Callable[[], t.Awaitable[t.Optional[ResponseReturnValue]]],
 ]
-ShellContextProcessorCallable = t.Callable[[], t.Dict[str, t.Any]]
+ShellContextProcessorCallable = t.Callable[[], dict[str, t.Any]]
 TeardownCallable = t.Union[
     t.Callable[[t.Optional[BaseException]], None],
     t.Callable[[t.Optional[BaseException]], t.Awaitable[None]],
 ]
 TemplateContextProcessorCallable = t.Union[
-    t.Callable[[], t.Dict[str, t.Any]],
+    t.Callable[[], dict[str, t.Any]],
-    t.Callable[[], t.Awaitable[t.Dict[str, t.Any]]],
+    t.Callable[[], t.Awaitable[dict[str, t.Any]]],
 ]
 TemplateFilterCallable = t.Callable[..., t.Any]
 TemplateGlobalCallable = t.Callable[..., t.Any]
 TemplateTestCallable = t.Callable[..., bool]
-URLDefaultCallable = t.Callable[[str, t.Dict[str, t.Any]], None]
+URLDefaultCallable = t.Callable[[str, dict[str, t.Any]], None]
 URLValuePreprocessorCallable = t.Callable[
-    [t.Optional[str], t.Optional[t.Dict[str, t.Any]]], None
+    [t.Optional[str], t.Optional[dict[str, t.Any]]], None
 ]
 
 # This should take Exception, but that either breaks typing the argument

tox.ini

@@ -1,9 +1,9 @@
 [tox]
 envlist =
-    py3{13,12,11,10,9,8}
+    py3{13,12,11,10,9}
     pypy310
     py312-min
-    py38-dev
+    py39-dev
     style
     typing
     docs