import numpy as npfrom sklearn import datasetsfrom sklearn.neighbors import KNeighborsClassifierfrom sklearn.model_selection import KFold # 主要用于K折交叉验证# 导入iris数据集iris = datasets.load_iris()X = iris.datay = iris.targetprint(X.shape,y.shape)# 定义想要搜索的K值，这里定义8个不同的值ks = [1,3,5,7,9,11,13,15]# 进行5折交叉验证，KFold返回的是每一折中训练数据和验证数据的index# 假设数据样本为：[1,3,5,6,11,12,43,12,44,2],总共10个样本# 则返回的kf的格式为（前面的是训练数据，后面的验证集）：# [0,1,3,5,6,7,8,9],[2,4]# [0,1,2,4,6,7,8,9],[3,5]# [1,2,3,4,5,6,7,8],[0,9]# [0,1,2,3,4,5,7,9],[6,8]# [0,2,3,4,5,6,8,9],[1,7]kf = KFold(n_splits = 5, random_state=2001, shuffle=True)# 保存当前最好的k值和对应的准确率best_k = ks[0]best_score = 0# 循环每一个k值for k in ks:    curr_score = 0    for train_index,valid_index in kf.split(X):        # 每一折的训练以及计算准确率        clf = KNeighborsClassifier(n_neighbors=k)        clf.fit(X[train_index],y[train_index])        curr_score = curr_score + clf.score(X[valid_index],y[valid_index])            # 求一下5折的平均准确率    avg_score = curr_score/5    if avg_score > best_score:        best_k = k        best_score = avg_score    print("current best score is :%.2f" % best_score,"best k:%d" %best_k)    print("after cross validation, the final best k is :%d" %best_k)