fix(flask): stop reading deprecated flask.__version__

Flask 3.1 deprecated the module-level __version__ attribute and emits a
DeprecationWarning on access; 3.2 will remove it. The Flask
instrumentor was hitting that warning at import time via

    _IS_FLASK_31_PLUS = hasattr(flask, "__version__") and
        package_version.parse(flask.__version__) >= package_version.parse("3.1.0")

even though it already computes the installed Flask version via
importlib.metadata.version("flask") a few lines below. Use that
flask_version for the 3.1+ check and drop the deprecated attribute
access entirely.

Fixes #4402

Signed-off-by: Ali <alliasgher123@gmail.com>

Author: alliasgher

CHANGELOG.md

@@ -11,6 +11,11 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## Unreleased
 
+### 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+
+  ([#4402](https://github.com/open-telemetry/opentelemetry-python-contrib/issues/4402))
+
 ### 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: