text: # -*- coding: utf-8 -*- {{{
  # vim: set fenc=utf-8 ft=python sw=4 ts=4 sts=4 et:
  #
  # Copyright 2019, Battelle Memorial Institute.
  #
  # Licensed 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 material was prepared as an account of work sponsored by an agency of
  # the United States Government. Neither the United States Government nor the
  # United States Department of Energy, nor Battelle, nor any of their
  # employees, nor any jurisdiction or organization that has cooperated in the
  # development of these materials, makes any warranty, express or
  # implied, or assumes any legal liability or responsibility for the accuracy,
  # completeness, or usefulness or any information, apparatus, product,
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  # favoring by the United States Government or any agency thereof, or
  # Battelle Memorial Institute. The views and opinions of authors expressed
  # herein do not necessarily state or reflect those of the
  # United States Government or any agency thereof.
  #
  # PACIFIC NORTHWEST NATIONAL LABORATORY operated by
  # BATTELLE for the UNITED STATES DEPARTMENT OF ENERGY
  # under Contract DE-AC05-76RL01830
  # }}}
  
  
  
  import re
  import weakref
  
  from volttron.platform import jsonapi
  
  from .base import SubsystemBase
  from ..errors import VIPError
  from ..results import ResultsDictionary
  from volttron.platform.vip.socket import Message
  
  __all__ = ['Query']
  
  
  class Query(SubsystemBase):
      def __init__(self, core):
          self.core = weakref.ref(core)
          self._results = ResultsDictionary()
          core.register('query', self._handle_result, self._handle_error)
  
      def query(self, prop: str, peer: str = ''):
          """ query a specific peer for a property value
  
          This method is very useful for retrieving configuration data from the core platform.  When
          peer is not specified it is defaulted to the router.
  
          :param prop:
              The property to query for.
          :param peer:
              The query to query upon
          :return:
          """
          connection = self.core().connection
          result = next(self._results)
          connection.send_vip(peer, 'query', args=[prop],
                              msg_id=result.ident)
          return result
  
      __call__ = query
  
      def _handle_result(self, message):
          if message.args and not message.args[0]:
              try:
                  result = self._results.pop(message.id)
              except KeyError:
                  return
              try:
                  value = message.args[1]
              except IndexError:
                  value = None
              result.set(value)
  
      def _handle_error(self, sender, message, error, **kwargs):
          try:
              result = self._results.pop(message.id)
          except KeyError:
              return
          result.set_exception(error)
  