'Construct an EvaluationMetrics object to store the evaluation metrics.
Args:
num_class: A positive integer specifying the number of classes.
top_k: A positive integer specifying how many predictions are considered per video.
Raises:
ValueError: An error occurred when MeanAveragePrecisionCalculator cannot
not be constructed.'

def __init__(self, num_class, top_k):

    self.sum_hit_at_one = 0.0
    self.sum_perr = 0.0
    self.sum_loss = 0.0
    self.map_calculator = map_calculator.MeanAveragePrecisionCalculator(num_class)
    self.global_ap_calculator = ap_calculator.AveragePrecisionCalculator()
    self.top_k = top_k
    self.num_examples = 0
