drop support for Python 3.8 (#5623)

.github/workflows/tests.yaml

@@ -20,7 +20,6 @@ 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: '3.9', tox: py-dev}

CHANGES.rst

@@ -3,6 +3,7 @@ Version 3.1.0
 
 Unreleased
 
+-   Drop support for Python 3.8. :pr:`5623`
 -   Provide a configuration option to control automatic option
     responses. :pr:`5496`
 -   ``Flask.open_resource``/``open_instance_resource`` and

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 +294,8 @@ 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, and 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

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/typing"]
 typeCheckingMode = "basic"
 

src/flask/app.py

@@ -1245,7 +1245,7 @@ def make_response(self, rv: ft.ResponseReturnValue) -> Response:
 
         # extend existing headers with provided headers
         if headers:
-            rv.headers.update(headers)  # type: ignore[arg-type]
+            rv.headers.update(headers)
 
         return rv
 

src/flask/config.py

@@ -150,23 +150,20 @@ def from_prefixed_env(
         .. versionadded:: 2.1
         """
         prefix = f"{prefix}_"
-        len_prefix = len(prefix)
 
         for key in sorted(os.environ):
             if not key.startswith(prefix):
                 continue
 
             value = os.environ[key]
+            key = key.removeprefix(prefix)
 
             try:
                 value = loads(value)
             except Exception:
                 # Keep the value as a string if loading failed.
                 pass
 
-            # Change to key.removeprefix(prefix) on Python >= 3.9.
-            key = key[len_prefix:]
-
             if "__" not in key:
                 # A non-nested key, set directly.
                 self[key] = value

src/flask/helpers.py

@@ -5,7 +5,7 @@
 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/sansio/scaffold.py

@@ -706,15 +706,6 @@ def _endpoint_from_view_func(view_func: ft.RouteCallable) -> str:
     return view_func.__name__
 
 
-def _path_is_relative_to(path: pathlib.PurePath, base: str) -> bool:
-    # Path.is_relative_to doesn't exist until Python 3.9
-    try:
-        path.relative_to(base)
-        return True
-    except ValueError:
-        return False
-
-
 def _find_package_path(import_name: str) -> str:
     """Find the path that contains the package or module."""
     root_mod_name, _, _ = import_name.partition(".")
@@ -745,7 +736,7 @@ def _find_package_path(import_name: str) -> str:
                 search_location = next(
                     location
                     for location in root_spec.submodule_search_locations
-                    if _path_is_relative_to(package_path, location)
+                    if package_path.is_relative_to(location)
                 )
             else:
                 # Pick the first path.
@@ -777,7 +768,7 @@ def find_package(import_name: str) -> tuple[str | None, str]:
     py_prefix = os.path.abspath(sys.prefix)
 
     # installed to the system
-    if _path_is_relative_to(pathlib.PurePath(package_path), py_prefix):
+    if pathlib.PurePath(package_path).is_relative_to(py_prefix):
         return py_prefix, package_path
 
     site_parent, site_folder = os.path.split(package_path)

src/flask/typing.py

@@ -12,7 +12,7 @@
     "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 @@
 
 # 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],
-    t.Tuple[ResponseValue, int],
-    t.Tuple[ResponseValue, int, HeadersValue],
+    tuple[ResponseValue, HeadersValue],
+    tuple[ResponseValue, int],
+    tuple[ResponseValue, int, HeadersValue],
     "WSGIApplication",
 ]
 
@@ -56,21 +56,21 @@
     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[[], t.Awaitable[t.Dict[str, t.Any]]],
+    t.Callable[[], 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

@@ -1,6 +1,6 @@
 [tox]
 envlist =
-    py3{13,12,11,10,9,8}
+    py3{13,12,11,10,9}
     pypy310
     py312-min
     py39-dev