deprecate __version__ attribute

CHANGES.rst

@@ -4,6 +4,8 @@ Version 3.0.0
 Unreleased
 
 -   Remove previously deprecated code. :pr:`5223`
+-   Deprecate the ``__version__`` attribute. Use feature detection, or
+    ``importlib.metadata.version("flask")``, instead. :issue:`5230`
 -   Restructure the code such that the Flask (app) and Blueprint
     classes have Sans-IO bases. :pr:`5127`
 

pyproject.toml

@@ -1,5 +1,6 @@
 [project]
 name = "Flask"
+version = "3.0.0.dev"
 description = "A simple framework for building complex web applications."
 readme = "README.rst"
 license = {file = "LICENSE.rst"}
@@ -26,7 +27,6 @@ dependencies = [
     "blinker>=1.6.2",
     "importlib-metadata>=3.6.0; python_version < '3.10'",
 ]
-dynamic = ["version"]
 
 [project.urls]
 Donate = "https://palletsprojects.com/donate"

src/flask/__init__.py

@@ -1,3 +1,7 @@
+from __future__ import annotations
+
+import typing as t
+
 from . import json as json
 from .app import Flask as Flask
 from .blueprints import Blueprint as Blueprint
@@ -38,4 +42,19 @@ from .templating import stream_template_string as stream_template_string
 from .wrappers import Request as Request
 from .wrappers import Response as Response
 
-__version__ = "3.0.0.dev"
+
+def __getattr__(name: str) -> t.Any:
+    if name == "__version__":
+        import importlib.metadata
+        import warnings
+
+        warnings.warn(
+            "The '__version__' attribute is deprecated and will be removed in"
+            " Flask 3.1. Use feature detection or"
+            " 'importlib.metadata.version(\"flask\")' instead.",
+            DeprecationWarning,
+            stacklevel=2,
+        )
+        return importlib.metadata.version("flask")
+
+    raise AttributeError(name)