'Revoke access to a CIDR range or EC2 SecurityGroup.
You need to pass in either a CIDR block or
an EC2 SecurityGroup from which to revoke access.
:type cidr_ip: string
:param cidr_ip: A valid CIDR IP range to revoke
:type ec2_group: :class:`boto.ec2.securitygroup.SecurityGroup`
:param ec2_group: An EC2 security group to revoke
:rtype: bool
:return: True if successful.'

def revoke(self, cidr_ip=None, ec2_group=None):

    if isinstance(ec2_group, SecurityGroup):
        group_name = ec2_group.name
        group_owner_id = ec2_group.owner_id
        return self.connection.revoke_dbsecurity_group(self.name, ec2_security_group_name=group_name, ec2_security_group_owner_id=group_owner_id)
    return self.connection.revoke_dbsecurity_group(self.name, cidr_ip=cidr_ip)
