机器学习用pandas提取数据后绘图报错

目前在学习机器学习的内容，找了一本书翻着看，找到一个对良性恶性肿瘤进行判断的例子，但是按照书中代码总是在绘图时报错，求解决方法。

##引用数据库
import numpy as np
import pandas as pd
import matplotlib.pyplot as plt
import scipy as sp

df_train=pd.read_csv('breast-cancer-train.csv')
df_test=pd.read_csv('breast-cancer-test.csv')

#选取“Clump Thickness”、“Cell Size”作为特征，构建测试集中的正负分类样本。
df_test_negative=df_test.loc[df_test['Type']==0],[['Clump Thickness','Cell Size']]
df_test_positive=df_test.loc[df_test['Type']==1],[['Clump Thickness','Cell Size']]

#绘制良性肿瘤样本点，标记为红色的⭕
plt.scatter(df_test_negative['Clump Thickness'],df_test_negative['Cell Size'],market='⭕',s=200,c='red')
#绘制恶性肿瘤样本点，标记为黑色的×
plt.scatter(df_test_positive['Clump Thickness'],df_test_positive['Cell Size'],market='×',s=150,c='black')

#绘制x,y轴的说明
plt.xlabel('Clump Thickness')
plt.ylabel('Cell Size')
#显示绘图结果
plt.show()

#报错信息
Traceback (most recent call last):
  File "D:\Pycharm basic\venv\机器学习.py", line 15, in <module>
    plt.scatter(df_test_negative['Clump Thickness'],df_test_negative['Cell Size'],market='⭕',s=200,c='red')
TypeError: tuple indices must be integers or slices, not str