无法使用pandas.read_excel覆盖数据

Question

此用于写入空单元格的代码有效：

fn = r'..\\..\\Decision Tree Classifier  TPS\\Decision Tree Classifier  TPS\\TestData.xlsx'    
df = pd.read_excel(fn, header=None)
df2 = pd.DataFrame({'Data': [7]})     
writer = pd.ExcelWriter(fn)
df.to_excel(writer, header=None, index=False)
df2.to_excel(writer, startcol=4,startrow=1, header=None, index=False)

writer.save()

此用于写入当前保存日期的单元格“ C2”的代码不：

fn = r'..\\..\\Decision Tree Classifier  TPS\\Decision Tree Classifier  TPS\\TestData.xlsx'
df = pd.read_excel(fn, header=None)    
df2 = pd.DataFrame({'Data': [7]}) 
writer = pd.ExcelWriter(fn)
df.to_excel(writer, header=None, index=False)

#change is located here
df2.to_excel(writer, startcol=3,startrow=1, header=None, index=False)

writer.save()

我该如何使用它？谢谢！