'Creates a new Security Group in EC2-Classic or a targeted VPC.
:param      name:        The name of the security group to create.
This must be unique.
:type       name:        ``str``
:param      description: Human readable description of a Security
Group.
:type       description: ``str``
:param      vpc_id:      Optional identifier for VPC networks
:type       vpc_id:      ``str``
:rtype: ``dict``'

def ex_create_security_group(self, name, description, vpc_id=None):

    params = {'Action': 'CreateSecurityGroup', 'GroupName': name, 'GroupDescription': description}
    if (vpc_id is not None):
        params['VpcId'] = vpc_id
    response = self.connection.request(self.path, params=params).object
    group_id = findattr(element=response, xpath='groupId', namespace=NAMESPACE)
    return {'group_id': group_id}
