fix(flask): stop reading deprecated flask.__version__

CHANGELOG.md

@@ -16,6 +16,11 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Bump `pylint` to `4.0.5`
   ([#4244](https://github.com/open-telemetry/opentelemetry-python-contrib/pull/4244))
 
+### Fixed
+
+- `opentelemetry-instrumentation-flask`: Stop reading the deprecated `flask.__version__` attribute; resolve the Flask version via `importlib.metadata` only so import no longer emits a `DeprecationWarning` under Flask 3.1+
+  ([#4422](https://github.com/open-telemetry/opentelemetry-python-contrib/pull/4422))
+
 ### Breaking changes
 
 - Drop Python 3.9 support

instrumentation/opentelemetry-instrumentation-flask/src/opentelemetry/instrumentation/flask/__init__.py

@@ -301,10 +301,6 @@ def response_hook(span: Span, status: str, response_headers: List):
 )
 
 _logger = getLogger(__name__)
-# Global constants for Flask 3.1+ streaming context cleanup
-_IS_FLASK_31_PLUS = hasattr(flask, "__version__") and package_version.parse(
-    flask.__version__
-) >= package_version.parse("3.1.0")
 
 _ENVIRON_STARTTIME_KEY = "opentelemetry-flask.starttime_key"
 _ENVIRON_SPAN_KEY = "opentelemetry-flask.span_key"
@@ -314,8 +310,16 @@ def response_hook(span: Span, status: str, response_headers: List):
 
 _excluded_urls_from_env = get_excluded_urls("FLASK")
 
+# Use importlib.metadata rather than flask.__version__: the latter has been
+# deprecated in Flask 3.1 and emits a DeprecationWarning on import; it is
+# scheduled for removal in Flask 3.2.
 flask_version = version("flask")
 
+# Global constant for Flask 3.1+ streaming context cleanup.
+_IS_FLASK_31_PLUS = package_version.parse(
+    flask_version
+) >= package_version.parse("3.1.0")
+
 if package_version.parse(flask_version) >= package_version.parse("2.2.0"):
 
     def _request_ctx_ref() -> weakref.ReferenceType:

instrumentation/opentelemetry-instrumentation-flask/tests/test_flask_compatibility.py

@@ -20,6 +20,7 @@
 import io
 import threading
 import time
+from importlib.metadata import version
 from unittest import mock, skipIf
 
 import flask
@@ -35,7 +36,7 @@
 class TestFlaskCompatibility(WsgiTestBase):
     def setUp(self):
         super().setUp()
-        self.flask_version = flask.__version__
+        self.flask_version = version("flask")
 
     def test_streaming_response_context_cleanup(self):
         """Test that streaming responses properly clean up context"""