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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 create_node(kwargs):
    '''
    Convenience function to make the rest api call for node creation.
    '''
    if not isinstance(kwargs, dict):
        kwargs = {}

    # Required parameters
    params = {
        'Action': 'CreateInstance',
        'InstanceType': kwargs.get('size_id', ''),
        'RegionId': kwargs.get('region_id', DEFAULT_LOCATION),
        'ImageId': kwargs.get('image_id', ''),
        'SecurityGroupId': kwargs.get('securitygroup_id', ''),
        'InstanceName': kwargs.get('name', ''),
    }

    # Optional parameters'
    optional = [
        'InstanceName', 'InternetChargeType',
        'InternetMaxBandwidthIn', 'InternetMaxBandwidthOut',
        'HostName', 'Password', 'SystemDisk.Category', 'VSwitchId'
        # 'DataDisk.n.Size', 'DataDisk.n.Category', 'DataDisk.n.SnapshotId'
    ]

    for item in optional:
        if item in kwargs:
            params.update({item: kwargs[item]})

    # invoke web call
    result = query(params)
    return result['InstanceId']