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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 revoke_dbsecurity_group(self, group_name, ec2_security_group_name=None, ec2_security_group_owner_id=None, cidr_ip=None):
 """ Remove an existing rule from an existing security group. You need to pass in either ec2_security_group_name and ec2_security_group_owner_id OR a CIDR block. :type group_name: string :param group_name: The name of the security group you are removing the rule from. :type ec2_security_group_name: string :param ec2_security_group_name: The name of the EC2 security group from which you are removing access. :type ec2_security_group_owner_id: string :param ec2_security_group_owner_id: The ID of the owner of the EC2 security from which you are removing access. :type cidr_ip: string :param cidr_ip: The CIDR block from which you are removing access. See http://en.wikipedia.org/wiki/Classless_Inter-Domain_Routing :rtype: bool :return: True if successful. """

        params = {'DBSecurityGroupName':group_name}
        if ec2_security_group_name:
            params['EC2SecurityGroupName'] = ec2_security_group_name
        if ec2_security_group_owner_id:
            params['EC2SecurityGroupOwnerId'] = ec2_security_group_owner_id
        if cidr_ip:
            params['CIDRIP'] = cidr_ip
        return self.get_object('RevokeDBSecurityGroupIngress', params,
                               DBSecurityGroup)