代码：

from sklearn.datasets import load_iris, fetch_20newsgroups
from sklearn.feature_extraction.text import TfidfVectorizer
from sklearn.model_selection import train_test_split, GridSearchCV
from sklearn.naive_bayes import MultinomialNB
from sklearn.neighbors import KNeighborsClassifier
from sklearn.preprocessing import StandardScaler
from sklearn.tree import DecisionTreeClassifier,export_graphviz


def knn_iris():
    # 用KNN 算法对鸢尾花进行分类
    # 1、获取数据
    iris = load_iris()
    # 2、划分数据集
    x_train,x_test,y_train,y_test = train_test_split(iris.data,iris.target,random_state=6)
    # 3、特征工程 - 标准化
    transfer = StandardScaler()
    x_train = transfer.fit_transform(x_train)
    x_test = transfer.transform(x_test)
    # 4、KNN 算法预估器
    estimator = KNeighborsClassifier(n_neighbors=3)
    estimator.fit(x_train,y_train)
    # 5、模型评估
    # 方法1 ：直接比对真实值和预测值
    y_predict = estimator.predict(x_test)
    print("y_predict：\n",y_predict)
    print("直接比对真实值和预测值：\n",y_test == y_predict)
    # 方法2：计算准确率
    score = estimator.score(x_test,y_test)
    print("准确率为：\n",score)
    return None

def knn_iris_gscv():
    # 用KNN 算法对鸢尾花进行分类，添加网格搜索和交叉验证
    # 1、获取数据
    iris = load_iris()

    # 2、划分数据集
    x_train,x_test,y_train,y_test = train_test_split(iris.data,iris.target,random_state=6)

    # 3、特征工程 - 标准化
    transfer = StandardScaler()
    x_train = transfer.fit_transform(x_train)
    x_test = transfer.transform(x_test)

    # 4、KNN 算法预估器
    estimator = KNeighborsClassifier()
    # 加入网格搜索和交叉验证
    # 参数准备
    param_dict = {"n_neighbors":[1,3,5,7,9,11]}
    estimator = GridSearchCV(estimator,param_grid=param_dict,cv=10)
    estimator.fit(x_train,y_train)

    # 5、模型评估
    # 方法1 ：直接比对真实值和预测值
    y_predict = estimator.predict(x_test)
    print("y_predict：\n",y_predict)
    print("直接比对真实值和预测值：\n",y_test == y_predict)
    # 方法2：计算准确率
    score = estimator.score(x_test,y_test)
    print("准确率为：\n",score)

    # 最佳参数：best_params_
    print("最佳参数：\n",estimator.best_params_)
    # 最佳结果：best_score_
    print("最佳结果：\n",estimator.best_score_)
    # 最佳估计值：best_estimator_
    print("最佳估计值：\n",estimator.best_estimator_)
    # 交叉验证结果：cv_results_
    print("交叉验证结果：\n",estimator.cv_results_)
    return None

def nb_news():
    # 用朴素贝叶斯算法对新闻进行分类
    # 1、获取数据
    news = fetch_20newsgroups(subset="all")
    # 2、划分数据集
    x_train,x_test,y_train,y_test = train_test_split(news.data,news.target)
    # 3、特征工程：文本特征抽取-tfidf
    transfer = TfidfVectorizer()
    x_train = transfer.fit_transform(x_train)
    x_test = transfer.transform(x_test)
    # 4、用朴素贝叶斯算法预估器流程
    estimator = MultinomialNB()
    estimator.fit(x_train,y_train)
    # 5、模型评估
    # 方法1 ：直接比对真实值和预测值
    y_predict = estimator.predict(x_test)
    print("y_predict：\n", y_predict)
    print("直接比对真实值和预测值：\n", y_test == y_predict)
    # 方法2：计算准确率
    score = estimator.score(x_test, y_test)
    print("准确率为：\n", score)
    return None

def decision_iris():
    # 用决策树对鸢尾花进行分类
    # 1、获取数据集
    iris = load_iris()
    # 2、划分数据集
    x_train,x_test,y_train,y_test = train_test_split(iris.data,iris.target,random_state=22)
    # 3、决策树预估器
    estimator = DecisionTreeClassifier(criterion="entropy")
    estimator.fit(x_train,y_train)
    # 4、模型评估
    # 方法1 ：直接比对真实值和预测值
    y_predict = estimator.predict(x_test)
    print("y_predict：\n", y_predict)
    print("直接比对真实值和预测值：\n", y_test == y_predict)
    # 方法2：计算准确率
    score = estimator.score(x_test, y_test)
    print("准确率为：\n", score)
    # 可视化决策树
    export_graphviz(estimator,out_file="iris_tree.dot",feature_names=iris.feature_names)
    return None

if __name__ == "__main__":
    # 代码1 ：用KNN算法对鸢尾花进行分类
    # knn_iris()
    # 代码2 ：用KNN算法对鸢尾花进行分类，添加网格搜索和交叉验证
    # knn_iris_gscv()
    # 代码3：用朴素贝叶斯算法对新闻进行分类
    # nb_news()
    # 代码4：用决策树对鸢尾花进行分类
    decision_iris()