Get runtime variables for policy interpolation.

        Runtime variables are merged with the passed in variables
        if any.

def get_variables(self, variables=None):
        """Get runtime variables for policy interpolation.

        Runtime variables are merged with the passed in variables
        if any.
        """
        # Global policy variable expansion, we have to carry forward on
        # various filter/action local vocabularies. Where possible defer
        # by using a format string.
        #
        # See https://github.com/capitalone/cloud-custodian/issues/2330
        if not variables:
            variables = {}

        if 'mode' in self.data:
            if 'role' in self.data['mode'] and not self.data['mode']['role'].startswith("arn:aws"):
                self.data['mode']['role'] = "arn:aws:iam::%s:role/%s" % \
                                            (self.options.account_id, self.data['mode']['role'])

        variables.update({
            # standard runtime variables for interpolation
            'account': '{account}',
            'account_id': self.options.account_id,
            'region': self.options.region,
            # non-standard runtime variables from local filter/action vocabularies
            #
            # notify action
            'policy': self.data,
            'event': '{event}',
            # mark for op action
            'op': '{op}',
            'action_date': '{action_date}',
            # tag action pyformat-date handling
            'now': utils.FormatDate(datetime.utcnow()),
            # account increase limit action
            'service': '{service}',
            # s3 set logging action :-( see if we can revisit this one.
            'bucket_region': '{bucket_region}',
            'bucket_name': '{bucket_name}',
            'source_bucket_name': '{source_bucket_name}',
            'target_bucket_name': '{target_bucket_name}',
            'target_prefix': '{target_prefix}',
            'LoadBalancerName': '{LoadBalancerName}'
        })
        return variables