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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def _callback_main(self, call, handler='edit_config', target='running', source='startup'):
 """ Callback for NETCONF calls. Args: call: An Element Tree element containing the XML of the NETCONF call you intend to make to the device. handler: Type of ncclient call to make. get_config: NETCONF standard get config. get: ncclient dispatch. For custom RPCs. edit_config: NETCONF standard edit. delete_config: NETCONF standard delete. copy_config: NETCONF standard copy. target: Target configuration location for action. Only used for edit_config, delete_config, and copy_config. source: Source of configuration information for copying configuration. Only used for copy_config. Returns: None Raises: None """

        try:
            if handler == 'get_config':
                call = ET.tostring(call.getchildren()[0])
                return self._mgr.get(filter=('subtree', call))

            call = ET.tostring(call)
            if handler == 'get':
                call_element = xml_.to_ele(call)
                return ET.fromstring(str(self._mgr.dispatch(call_element)))
            if handler == 'edit_config':
                self._mgr.edit_config(target=target, config=call)
            if handler == 'delete_config':
                self._mgr.delete_config(target=target)
            if handler == 'copy_config':
                self._mgr.copy_config(target=target, source=source)
        except (ncclient.transport.TransportError,
                ncclient.transport.SessionCloseError,
                ncclient.transport.SSHError,
                ncclient.transport.AuthenticationError,
                ncclient.transport.SSHUnknownHostError) as error:
            logging.error(error)
            raise DeviceCommError