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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']
[docs]class Query(SubsystemBase):
def __init__(self, core):
self.core = weakref.ref(core)
self._results = ResultsDictionary()
core.register('query', self._handle_result, self._handle_error)
[docs] 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)