Fix Flask version warning

logstash_async/formatter.py

@@ -4,6 +4,7 @@
 # of the MIT license.  See the LICENSE file for details.
 
 from datetime import date, datetime
+import importlib.metadata
 import logging
 import socket
 import sys
@@ -438,9 +439,7 @@ def __init__(self, *args, **kwargs):
 
     # ----------------------------------------------------------------------
     def _fetch_flask_version(self):
-        # pylint: disable-next=import-error,import-outside-toplevel,no-name-in-module
-        from flask import __version__
-        self._flask_version = __version__
+        self._flask_version = importlib.metadata.version('flask')
 
     # ----------------------------------------------------------------------
     def _get_extra_fields(self, record):

tests/formatter_test.py

@@ -7,6 +7,7 @@
 from logging import FileHandler, makeLogRecord
 from types import SimpleNamespace
 from unittest.mock import patch
+import importlib.metadata
 import os
 import socket
 import sys
@@ -354,10 +355,7 @@ class FlaskTestMixin:
     @classmethod
     def setUpClass(cls):  # pylint: disable=invalid-name
         super().setUpClass()
-
-        # pylint: disable-next=import-outside-toplevel,no-name-in-module
-        from flask import __version__
-        cls.flask_version = __version__
+        cls.flask_version = importlib.metadata.version('flask')
 
     def _create_request(self):
         return SimpleNamespace(