Warn about unsupported Python 3.10 (apache#19060)

Co-authored-by: Jed Cunningham <66968678+jedcunningham@users.noreply.github.com>

README.md

@@ -98,6 +98,8 @@ MariaDB is not tested/recommended.
 **Note**: SQLite is used in Airflow tests. Do not use it in production. We recommend
 using the latest stable version of SQLite for local development.
 
+**Note**: Python v3.10 is not supported yet. For details, see [#19059](https://github.com/apache/airflow/issues/19059).
+
 ## Getting started
 
 Visit the official Airflow website documentation (latest **stable** release) for help with

airflow/__init__.py

@@ -36,7 +36,7 @@
 
 __version__ = version.version
 
-__all__ = ['__version__', 'login', 'DAG', 'PY36', 'PY37', 'PY38', 'PY39']
+__all__ = ['__version__', 'login', 'DAG', 'PY36', 'PY37', 'PY38', 'PY39', 'PY310']
 
 # Make `airflow` an namespace package, supporting installing
 # airflow.providers.* in different locations (i.e. one in site, and one in user
@@ -51,6 +51,7 @@
 PY37 = sys.version_info >= (3, 7)
 PY38 = sys.version_info >= (3, 8)
 PY39 = sys.version_info >= (3, 9)
+PY310 = sys.version_info >= (3, 10)
 
 
 def __getattr__(name):

airflow/__main__.py

@@ -19,20 +19,28 @@
 # under the License.
 
 """Main executable module"""
-
 import os
+import warnings
 
 import argcomplete
 
+from airflow import PY310
 from airflow.cli import cli_parser
 from airflow.configuration import conf
+from airflow.utils.docs import get_docs_url
 
 
 def main():
     """Main executable function"""
     if conf.get("core", "security") == 'kerberos':
         os.environ['KRB5CCNAME'] = conf.get('kerberos', 'ccache')
         os.environ['KRB5_KTNAME'] = conf.get('kerberos', 'keytab')
+    if PY310:
+        docs_url = get_docs_url('installation/prerequisites.html')
+        warnings.warn(
+            "Python v3.10 is not official supported on this version of Airflow. Please be careful. "
+            f"For details, see: {docs_url}"
+        )
 
     parser = cli_parser.get_parser()
     argcomplete.autocomplete(parser)

docs/apache-airflow/installation/prerequisites.rst

@@ -37,6 +37,8 @@ running multiple schedulers -- please see: :doc:`/concepts/scheduler`. MariaDB i
 **Note:** SQLite is used in Airflow tests. Do not use it in production. We recommend
 using the latest stable version of SQLite for local development.
 
+**Note**: Python v3.10 is not supported yet. For details, see `#19059 <https://github.com/apache/airflow/issues/19059>`__.
+
 Starting with Airflow 2.1.2, Airflow is tested with Python 3.6, 3.7, 3.8, and 3.9.
 
 The minimum memory required we recommend Airflow to run with is 4GB, but the actual requirements depends