查准率/正确率 :
P = T P T P + F P P=\frac{TP}{TP+FP} P=TP+FPTP​
查全率/召回率 :
R = T P T P + F N R=\frac{TP}{TP+FN} R=TP+FNTP​
F值：正确率和召回率的调和平均值
F 1 = 2 P R P + R F1 = \frac{2PR}{P+R} F1=P+R2PR​

def precision_recall(gt, preds):
    '''
    input: gt(ground_truth), preds(predictions)
    output: precision, recall
    '''
    TP = 0
    FP = 0
    FN = 0
    for t in gt:
        if t in preds:
            TP += 1
        else:
            FN += 1
    for p in preds:
        if p not in gt:
            FP += 1
    if TP+FP == 0:
        precision = 0
    else:
        precision = TP/float(TP+FP)
    if TP+FN == 0:
        recall = 0
    else:
        recall = TP/float(TP+FN)
    return precision, recall