class_docstr: This handler handles connection and exectuin of Google BigQuery statements
docstr: Handles the connection to a BigQuery
docstr_tok: ["Handles","the","connection","to","a","BigQuery"]
code: def connect(self):
      """
      Handles the connection to a BigQuery
      """
      if self.is_connected is True:
          return self.client
  
      info = self._get_account_keys()
      storage_credentials = (
          service_account.Credentials.from_service_account_info(info)
      )
      client = bigquery.Client(
          project=self.connection_data["project_id"],
          credentials=storage_credentials,
      )
      self.is_connected = True
      self.client = client
      return self.client
  
imports: import os
  import json
  from collections import OrderedDict
  from google.cloud import bigquery
  from google.oauth2 import service_account
  from sqlalchemy_bigquery.base import BigQueryDialect
  from mindsdb_sql.parser.ast.base import ASTNode
  from mindsdb_sql.render.sqlalchemy_render import SqlalchemyRender
  from mindsdb.integrations.libs.base import DatabaseHandler
  from mindsdb.integrations.libs.const import HANDLER_CONNECTION_ARG_TYPE
  from mindsdb.integrations.libs.response import HandlerStatusResponse, HandlerResponse, RESPONSE_TYPE
  from mindsdb.utilities import log
label_desc: Use image node_id 4 for calling the BigQueryHandler obj's underlying member method code with example usage: obj.connect() and returns: self, self