content: # -*- coding: utf-8 -*-
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  # 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
  #
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  # 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.
  
  from __future__ import absolute_import
  from __future__ import division
  from __future__ import print_function
  from __future__ import unicode_literals
  
  import os
  import random
  
  from airflow.models import Connection
  from airflow.exceptions import AirflowException
  from airflow.utils.db import provide_session
  from airflow.utils.log.logging_mixin import LoggingMixin
  
  CONN_ENV_PREFIX = 'AIRFLOW_CONN_'
  
  
  class BaseHook(LoggingMixin):
      """
      Abstract base class for hooks, hooks are meant as an interface to
      interact with external systems. MySqlHook, HiveHook, PigHook return
      object that can handle the connection and interaction to specific
      instances of these systems, and expose consistent methods to interact
      with them.
      """
      def __init__(self, source):
          pass
  
      @classmethod
      @provide_session
      def _get_connections_from_db(cls, conn_id, session=None):
          db = (
              session.query(Connection)
              .filter(Connection.conn_id == conn_id)
              .all()
          )
          session.expunge_all()
          if not db:
              raise AirflowException(
                  "The conn_id `{0}` isn't defined".format(conn_id))
          return db
  
      @classmethod
      def _get_connection_from_env(cls, conn_id):
          environment_uri = os.environ.get(CONN_ENV_PREFIX + conn_id.upper())
          conn = None
          if environment_uri:
              conn = Connection(conn_id=conn_id, uri=environment_uri)
          return conn
  
      @classmethod
      def get_connections(cls, conn_id):
          conn = cls._get_connection_from_env(conn_id)
          if conn:
              conns = [conn]
          else:
              conns = cls._get_connections_from_db(conn_id)
          return conns
  
      @classmethod
      def get_connection(cls, conn_id):
          conn = random.choice(cls.get_connections(conn_id))
          if conn.host:
              log = LoggingMixin().log
              log.info("Using connection to: %s", conn.host)
          return conn
  
      @classmethod
      def get_hook(cls, conn_id):
          connection = cls.get_connection(conn_id)
          return connection.get_hook()
  
      def get_conn(self):
          raise NotImplementedError()
  
      def get_records(self, sql):
          raise NotImplementedError()
  
      def get_pandas_df(self, sql):
          raise NotImplementedError()
  
      def run(self, sql):
          raise NotImplementedError()
  