deprecate __version__

CHANGES.rst

@@ -6,6 +6,8 @@ Unreleased
 -   Use modern packaging metadata with ``pyproject.toml`` instead of ``setup.cfg``.
     :pr:`326`
 -   Use ``flit_core`` instead of ``setuptools`` as build backend.
+-   Deprecate the ``__version__`` attribute. Use feature detection, or
+    ``importlib.metadata.version("itsdangerous")``, instead. :issue:`2770`
 
 
 Version 2.1.2

pyproject.toml

@@ -1,5 +1,6 @@
 [project]
 name = "itsdangerous"
+version = "2.2.0.dev"
 description = "Safely pass data to untrusted environments and back."
 readme = "README.md"
 license = { file = "LICENSE.txt" }
@@ -13,7 +14,6 @@ classifiers = [
     "Typing :: Typed",
 ]
 requires-python = ">=3.7"
-dynamic = ["version"]
 
 [project.urls]
 Donate = "https://palletsprojects.com/donate"

src/itsdangerous/__init__.py

@@ -1,3 +1,7 @@
+from __future__ import annotations
+
+import typing as t
+
 from .encoding import base64_decode as base64_decode
 from .encoding import base64_encode as base64_encode
 from .encoding import want_bytes as want_bytes
@@ -16,4 +20,19 @@
 from .url_safe import URLSafeSerializer as URLSafeSerializer
 from .url_safe import URLSafeTimedSerializer as URLSafeTimedSerializer
 
-__version__ = "2.2.0.dev0"
+
+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"
+            " ItsDangerous 2.3. Use feature detection or"
+            " 'importlib.metadata.version(\"itsdangerous\")' instead.",
+            DeprecationWarning,
+            stacklevel=2,
+        )
+        return importlib.metadata.version("itsdangerous")
+
+    raise AttributeError(name)