`flask.__version__` is deprecated

[davidism]

Describe your environment

OS: Any
Python version: Any
Package version: 0.61b0

What happened?

The flask.__version__ attribute is deprecated and will be removed, it raises a DeprecationWarning on access.

.tox/tests/lib/python3.14/site-packages/app/telemetry.py:9: in <module>
    from opentelemetry.instrumentation.flask import FlaskInstrumentor
.tox/tests/lib/python3.14/site-packages/opentelemetry/instrumentation/flask/__init__.py:306: in <module>
    _IS_FLASK_31_PLUS = hasattr(flask, "__version__") and package_version.parse(
                        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
.tox/tests/lib/python3.14/site-packages/flask/__init__.py:52: in __getattr__
    warnings.warn(
DeprecationWarning: The '__version__' attribute is deprecated and will be removed in Flask 3.2. Use feature detection or 'importlib.metadata.version("flask")' instead.

Steps to Reproduce

from opentelemetry.instrumentation.flask import FlaskInstrumentor

Expected Result

No deprecation warning is emitted.

Actual Result

A deprecation warning is emitted.

Additional context

The code that causes this was added recently in #3938:

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

Lines 305 to 308 in 0f92478

	# 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")

However, it ignores the existing flask_version attribute defined a few lines below, which was added to address this warning the first time it was reported:

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

Line 318 in 0f92478

flask_version = version("flask")

The version 3.1 detection should be moved below this line, and use the existing metadata rather than trying to access flask.__version__ again.

Would you like to implement a fix?

None

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