Turn Pydantic into an optional depenedency

We've been internally using pydantic for internal API and it caused
some compatibility issues, because Pydantic is so popular and currently
still users of Pydantic are somewhat split between Pydantic 1 and
Pydantic 2.  The popularity of Pydantic works against us, and since we
are not yet using it in "production" (and in the future we will only
actually use it for Internal API), it seems that turning Pydantic into
an optional dependency is the best way we can proceed.

It's as simple as converting all the direct imports into a common util
imports that have a fallback mechanism when import is not found.

This should enable less conflicts when installing 3rd-party libraries
with Airflow.

.github/workflows/ci.yml

@@ -1277,6 +1277,56 @@ jobs:
         uses: ./.github/actions/post_tests_failure
         if: failure()
 
+  tests-postgres-no-pydantic:
+    timeout-minutes: 130
+    name: >
+      DB:NoPydantic${{needs.build-info.outputs.default-postgres-version}},
+      Py${{needs.build-info.outputs.default-python-version}}:
+      ${{needs.build-info.outputs.parallel-test-types-list-as-string}}
+    runs-on: ${{fromJSON(needs.build-info.outputs.runs-on)}}
+    needs: [build-info, wait-for-ci-images]
+    env:
+      RUNS_ON: "${{needs.build-info.outputs.runs-on}}"
+      PARALLEL_TEST_TYPES: "${{needs.build-info.outputs.parallel-test-types-list-as-string}}"
+      PR_LABELS: "${{needs.build-info.outputs.pull-request-labels}}"
+      FULL_TESTS_NEEDED: "${{needs.build-info.outputs.full-tests-needed}}"
+      DEBUG_RESOURCES: "${{needs.build-info.outputs.debug-resources}}"
+      BACKEND: "postgres"
+      ENABLE_COVERAGE: "${{needs.build-info.outputs.run-coverage}}"
+      PYTHON_MAJOR_MINOR_VERSION: "${{needs.build-info.outputs.default-python-version}}"
+      PYTHON_VERSION: "${needs.build-info.outputs.default-python-version}}"
+      POSTGRES_VERSION: "${{needs.build-info.outputs.default-postgres-version}}"
+      BACKEND_VERSION: "${{needs.build-info.outputs.default-postgres-version}}"
+      NO_PYDANTIC: "true"
+      JOB_ID: >
+        postgres-nopydantic-${{needs.build-info.outputs.default-python-version}}-
+        ${{needs.build-info.outputs.default-postgres-version}}
+    if: needs.build-info.outputs.run-tests == 'true'
+    steps:
+      - name: Cleanup repo
+        shell: bash
+        run: docker run -v "${GITHUB_WORKSPACE}:/workspace" -u 0:0 bash -c "rm -rf /workspace/*"
+      - name: "Checkout ${{ github.ref }} ( ${{ github.sha }} )"
+        uses: actions/checkout@v4
+        with:
+          persist-credentials: false
+      - name: >
+          Prepare breeze & CI image: ${{needs.build-info.outputs.default-python-version}}:${{env.IMAGE_TAG}}
+        uses: ./.github/actions/prepare_breeze_and_image
+      - name: >
+          Tests: ${{matrix.python-version}}:${{needs.build-info.outputs.parallel-test-types-list-as-string}}
+        run: >
+          breeze testing db-tests
+          --parallel-test-types "${{needs.build-info.outputs.parallel-test-types-list-as-string}}"
+      - name: >
+          Post Tests success: ${{needs.build-info.outputs.default-python-version}}:Boto"
+        uses: ./.github/actions/post_tests_success
+        if: success()
+      - name: >
+          Post Tests failure: ${{needs.build-info.outputs.default-python-version}}:Boto"
+        uses: ./.github/actions/post_tests_failure
+        if: failure()
+
   tests-postgres-pendulum-2:
     timeout-minutes: 130
     name: >

Dockerfile.ci

@@ -897,6 +897,18 @@ function check_boto_upgrade() {
     pip check
 }
 
+function check_no_pydantic() {
+    if [[ ${NO_PYDANTIC=} != "true" ]]; then
+        return
+    fi
+    echo
+    echo "${COLOR_BLUE}Remove pydantic${COLOR_RESET}"
+    echo
+    pip uninstall --root-user-action ignore pydantic -y || true
+    pip check
+}
+
+
 function check_download_sqlalchemy() {
     if [[ ${DOWNGRADE_SQLALCHEMY=} != "true" ]]; then
         return
@@ -949,6 +961,7 @@ function check_run_tests() {
 determine_airflow_to_use
 environment_initialization
 check_boto_upgrade
+check_no_pydantic
 check_download_sqlalchemy
 check_download_pendulum
 check_run_tests "${@}"

INSTALL

@@ -253,10 +253,10 @@ gcp_api, github, github-enterprise, google, google-auth, graphviz, grpc, hashico
 http, imap, influxdb, jdbc, jenkins, kerberos, kubernetes, ldap, leveldb, microsoft-azure,
 microsoft-mssql, microsoft-psrp, microsoft-winrm, mongo, mssql, mysql, neo4j, odbc, openai,
 openfaas, openlineage, opensearch, opsgenie, oracle, otel, pagerduty, pandas, papermill, password,
-pgvector, pinecone, pinot, postgres, presto, qdrant, rabbitmq, redis, s3, s3fs, salesforce, samba,
-saml, segment, sendgrid, sentry, sftp, singularity, slack, smtp, snowflake, spark, sqlite, ssh,
-statsd, tableau, tabular, telegram, trino, vertica, virtualenv, weaviate, webhdfs, winrm, yandex,
-zendesk
+pgvector, pinecone, pinot, postgres, presto, pydantic, qdrant, rabbitmq, redis, s3, s3fs,
+salesforce, samba, saml, segment, sendgrid, sentry, sftp, singularity, slack, smtp, snowflake,
+spark, sqlite, ssh, statsd, tableau, tabular, telegram, trino, vertica, virtualenv, weaviate,
+webhdfs, winrm, yandex, zendesk
 
 # END REGULAR EXTRAS HERE
 

airflow/providers/apache/hdfs/sensors/hdfs.py

@@ -18,6 +18,8 @@
 
 from airflow.sensors.base import BaseSensorOperator
 
+# Ignore missing docstring
+
 _EXCEPTION_MESSAGE = """The old HDFS Sensors have been removed in 4.0.0 version of the apache.hdfs provider.
 Please convert your DAGs to use the WebHdfsSensor or downgrade the provider to below 4.*
 if you want to continue using it.

airflow/providers/papermill/hooks/kernel.py

@@ -16,17 +16,14 @@
 # under the License.
 from __future__ import annotations
 
-from typing import TYPE_CHECKING
+import typing
 
 from jupyter_client import AsyncKernelManager
 from papermill.clientwrap import PapermillNotebookClient
 from papermill.engines import NBClientEngine
 from papermill.utils import merge_kwargs, remove_args
 from traitlets import Unicode
 
-if TYPE_CHECKING:
-    from pydantic import typing
-
 from airflow.hooks.base import BaseHook
 
 JUPYTER_KERNEL_SHELL_PORT = 60316

airflow/serialization/pydantic/dag.py

@@ -21,17 +21,17 @@
 from typing import Any, List, Optional
 
 from dateutil import relativedelta
-from pydantic import (
+from typing_extensions import Annotated
+
+from airflow import DAG, settings
+from airflow.configuration import conf as airflow_conf
+from airflow.utils.pydantic import (
     BaseModel as BaseModelPydantic,
     ConfigDict,
     PlainSerializer,
     PlainValidator,
     ValidationInfo,
 )
-from typing_extensions import Annotated
-
-from airflow import DAG, settings
-from airflow.configuration import conf as airflow_conf
 from airflow.utils.sqlalchemy import Interval
 
 

airflow/serialization/pydantic/dag_run.py

@@ -19,10 +19,9 @@
 from datetime import datetime
 from typing import TYPE_CHECKING, Iterable, List, Optional
 
-from pydantic import BaseModel as BaseModelPydantic, ConfigDict
-
 from airflow.serialization.pydantic.dag import PydanticDag
 from airflow.serialization.pydantic.dataset import DatasetEventPydantic
+from airflow.utils.pydantic import BaseModel as BaseModelPydantic, ConfigDict
 from airflow.utils.session import NEW_SESSION, provide_session
 
 if TYPE_CHECKING:
@@ -101,4 +100,10 @@ def get_task_instance(
         )
 
 
-DagRunPydantic.model_rebuild()
+try:
+    import pydantic  # noqa: F401
+
+    # Only run this is pydantic is installed
+    DagRunPydantic.model_rebuild()
+except ImportError:
+    pass

airflow/serialization/pydantic/dataset.py

@@ -17,7 +17,7 @@
 from datetime import datetime
 from typing import List, Optional
 
-from pydantic import BaseModel as BaseModelPydantic, ConfigDict
+from airflow.utils.pydantic import BaseModel as BaseModelPydantic, ConfigDict
 
 
 class DagScheduleDatasetReferencePydantic(BaseModelPydantic):

airflow/serialization/pydantic/job.py

@@ -18,10 +18,9 @@
 from functools import cached_property
 from typing import Optional
 
-from pydantic import BaseModel as BaseModelPydantic, ConfigDict
-
 from airflow.executors.executor_loader import ExecutorLoader
 from airflow.jobs.base_job_runner import BaseJobRunner
+from airflow.utils.pydantic import BaseModel as BaseModelPydantic, ConfigDict
 
 
 def check_runner_initialized(job_runner: Optional[BaseJobRunner], job_type: str) -> BaseJobRunner:

airflow/serialization/pydantic/taskinstance.py

@@ -19,7 +19,6 @@
 from datetime import datetime
 from typing import TYPE_CHECKING, Any, Iterable, Optional
 
-from pydantic import BaseModel as BaseModelPydantic, ConfigDict, PlainSerializer, PlainValidator
 from typing_extensions import Annotated
 
 from airflow.models import Operator
@@ -29,16 +28,17 @@
 from airflow.serialization.pydantic.dag_run import DagRunPydantic
 from airflow.utils.log.logging_mixin import LoggingMixin
 from airflow.utils.net import get_hostname
+from airflow.utils.pydantic import BaseModel as BaseModelPydantic, ConfigDict, PlainSerializer, PlainValidator
 from airflow.utils.session import NEW_SESSION, provide_session
 from airflow.utils.xcom import XCOM_RETURN_KEY
 
 if TYPE_CHECKING:
     import pendulum
-    from pydantic_core.core_schema import ValidationInfo
     from sqlalchemy.orm import Session
 
     from airflow.models.dagrun import DagRun
     from airflow.utils.context import Context
+    from airflow.utils.pydantic import ValidationInfo
     from airflow.utils.state import DagRunState
 
 
@@ -430,4 +430,10 @@ def command_as_list(
         )
 
 
-TaskInstancePydantic.model_rebuild()
+try:
+    import pydantic  # noqa: F401
+
+    # Only run this is pydantic is installed
+    TaskInstancePydantic.model_rebuild()
+except ImportError:
+    pass

airflow/serialization/pydantic/tasklog.py

@@ -16,7 +16,7 @@
 # under the License.
 from datetime import datetime
 
-from pydantic import BaseModel as BaseModelPydantic, ConfigDict
+from airflow.utils.pydantic import BaseModel as BaseModelPydantic, ConfigDict
 
 
 class LogTemplatePydantic(BaseModelPydantic):

airflow/serialization/serialized_objects.py

@@ -70,15 +70,14 @@
 if TYPE_CHECKING:
     from inspect import Parameter
 
-    from pydantic import BaseModel
-
     from airflow.models.baseoperatorlink import BaseOperatorLink
     from airflow.models.expandinput import ExpandInput
     from airflow.models.operator import Operator
     from airflow.models.taskmixin import DAGNode
     from airflow.serialization.json_schema import Validator
     from airflow.ti_deps.deps.base_ti_dep import BaseTIDep
     from airflow.timetables.base import Timetable
+    from airflow.utils.pydantic import BaseModel
 
     HAS_KUBERNETES: bool
     try:

airflow/utils/pydantic.py

@@ -0,0 +1,53 @@
+# Licensed to the Apache Software Foundation (ASF) under one
+# or more contributor license agreements.  See the NOTICE file
+# distributed with this work for additional information
+# regarding copyright ownership.  The ASF licenses this file
+# to you under the Apache License, Version 2.0 (the
+# "License"); you may not use this file except in compliance
+# with the License.  You may obtain a copy of the License at
+#
+#   http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing,
+# software distributed under the License is distributed on an
+# "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+# KIND, either express or implied.  See the License for the
+# specific language governing permissions and limitations
+# under the License.
+
+# This is an util module that makes Pydantic use optional. While we are using Pydantic in the airflow core
+# codebase, we don't want to make it a hard dependency for all the users of the core codebase, because
+# it is only used in the serialization and deserialization of the models for Internal API and for nothing
+# else, and since Pydantic is a very popular library, we don't want to force the users of the core codebase
+# to install specific Pydantic version - especially that a lot of libraries out there still depend on
+# Pydantic 1 and our internal API uses Pydantic 2+
+
+from __future__ import annotations
+
+try:
+    from pydantic import BaseModel, ConfigDict, PlainSerializer, PlainValidator, ValidationInfo
+except ImportError:
+
+    class BaseModel:  # type: ignore[no-redef]  # noqa
+        def __init__(self, *args, **kwargs):
+            pass
+
+    class ConfigDict:  # type: ignore[no-redef]  # noqa
+        def __init__(self, *args, **kwargs):
+            pass
+
+    class PlainSerializer:  # type: ignore[no-redef]  # noqa
+        def __init__(self, *args, **kwargs):
+            pass
+
+    class PlainSerializer:  # type: ignore[no-redef]  # noqa
+        def __init__(self, *args, **kwargs):
+            pass
+
+    class PlainValidator:  # type: ignore[no-redef]  # noqa
+        def __init__(self, *args, **kwargs):
+            pass
+
+    class ValidationInfo:  # type: ignore[no-redef]  # noqa
+        def __init__(self, *args, **kwargs):
+            pass

contributing-docs/12_airflow_dependencies_and_extras.rst

@@ -209,10 +209,10 @@ gcp_api, github, github-enterprise, google, google-auth, graphviz, grpc, hashico
 http, imap, influxdb, jdbc, jenkins, kerberos, kubernetes, ldap, leveldb, microsoft-azure,
 microsoft-mssql, microsoft-psrp, microsoft-winrm, mongo, mssql, mysql, neo4j, odbc, openai,
 openfaas, openlineage, opensearch, opsgenie, oracle, otel, pagerduty, pandas, papermill, password,
-pgvector, pinecone, pinot, postgres, presto, qdrant, rabbitmq, redis, s3, s3fs, salesforce, samba,
-saml, segment, sendgrid, sentry, sftp, singularity, slack, smtp, snowflake, spark, sqlite, ssh,
-statsd, tableau, tabular, telegram, trino, vertica, virtualenv, weaviate, webhdfs, winrm, yandex,
-zendesk
+pgvector, pinecone, pinot, postgres, presto, pydantic, qdrant, rabbitmq, redis, s3, s3fs,
+salesforce, samba, saml, segment, sendgrid, sentry, sftp, singularity, slack, smtp, snowflake,
+spark, sqlite, ssh, statsd, tableau, tabular, telegram, trino, vertica, virtualenv, weaviate,
+webhdfs, winrm, yandex, zendesk
 
   .. END REGULAR EXTRAS HERE