想编写一个自动创建各个科室的业务的excel程序（python）

import pandas as pd
import tkinter.filedialog
import tkinter.simpledialog
import shutil
import xlwings as xw

app = xw.App(visible= False,add_book= False)

sques = ("一病区","二病区") 
#病区信息
         

months = input("输入生成月份") + "月"  
#输入需要创建的月份

path = tkinter.filedialog.askopenfilename() 
#弹出选择原始文件路径
df_gr = pd.read_excel(path,sheet_name="当前数据库") 
#读取原始文件中名为“当前数据库”的表中的信息

#savepath = tkinter.filedialog.askdirectory()
 #这里准备自定义存储位置 
# 引入循环，创建各个科室的excel文件
for sque in sques:
    tar_excel = f"{sque}{months}重点监控指标分析.xlsx"
    shutil.copy("下发模板.xlsx", tar_excel) #模板文件确定样式
    workbook = app.books.open(tar_excel)
    worksheet = workbook.sheets[0]
    worksheet['A2'].value = worksheet['A2'].value.replace("m", months) #将模板文件中的字母代替为相应的月份
    worksheet['C2'].value = worksheet['C2'].value.replace("s", sque)  #将模板文件中的字母代替为相应的科室
    workbook.save()
    workbook.close()

#将数据库中属于现在科室的数据全部提取出来
    df_c = df_gr["病区"] == sque  
    count = 0
    for tiaojian in df_gr["病区"]:
        count = count + 1              
#提取数据的行数，因为head（）函数默认返回值为5，而我们的数据条数大于5，甚至可能是变量

    df_copy = df_gr[df_c].head(count)  
#将符合要求的数值提取出来
#此处原意是想在sheet3中写入上面取出的数据，但是如果存在sheet3（模板文件中存在sheet3），代码就会报错，求解答
    with pd.ExcelWriter(tar_excel, mode='a', engine='openpyxl') as writer:    
        writer.sheets = {ws.title: ws for ws in writer.book.worksheets}
        df_copy.to_excel(writer, sheet_name="Sheet3", index=False)

app.quit()

#错误代码：输入生成月份1
Traceback (most recent call last):
File "D:/xx/xx/xx/Python/newpython/zidingyihanshu.py", line 41, in
df_copy.to_excel(writer, sheet_name="Sheet3", index=False)
File "C:\Users\Administrator\AppData\Local\Programs\Python\Python37\lib\site-packages\pandas\core\generic.py", line 2291, in to_excel
storage_options=storage_options,
File "C:\Users\Administrator\AppData\Local\Programs\Python\Python37\lib\site-packages\pandas\io\formats\excel.py", line 845, in write
freeze_panes=freeze_panes,
File "C:\Users\Administrator\AppData\Local\Programs\Python\Python37\lib\site-packages\pandas\io\excel_openpyxl.py", line 437, in write_cells
f"Sheet '{sheet_name}' already exists and "
ValueError: Sheet 'Sheet3' already exists and if_sheet_exists is set to 'error'.

Process finished with exit code 1