如何在不同的文件夹中合并两个同名的excel文件？

Question

   from collections import defaultdict
from glob import glob
from itertools import chain, groupby
import pandas as pd
from pandas import ExcelWriter
from pathlib import Path
from pprint import pprint, pformat
from textwrap import indent
import os
import os.path
ca_2015= "D:\master concordia\DYD\Ecobee DYD\canada\Canada 2015"
ca_2016= "D:\master concordia\DYD\Ecobee DYD\canada\Canada 2016"
ca_2017= "D:\master concordia\DYD\Ecobee DYD\canada\Canada 2017"
ca_2018= "D:\master concordia\DYD\Ecobee DYD\canada\Canada 2018"
ca_2019= "D:\master concordia\DYD\Ecobee DYD\canada\Canada 2019"
files_2015 = os.listdir(ca_2015)
files_2016 = os.listdir(ca_2016)
files_2017 = os.listdir(ca_2017)
files_2018 = os.listdir(ca_2018)
files_2019 = os.listdir(ca_2019)
df_total= pd.DataFrame()

i=0
for file in files_2017:
    os.chdir("D:\master concordia\DYD\Ecobee DYD\canada\Canada 2017")
    if file in files_2018 and file in files_2019:
        df_file= pd.read_csv(file)
        df_total= pd.concat([df_file], ignore_index=True)
        for f in files_2018:
            os.chdir("D:\master concordia\DYD\Ecobee DYD\canada\Canada 2018")
            if f in files_2017 and f in files_2019:
                df_f= pd.read_csv(f)
                df_total= pd.concat([df_f], ignore_index=True)
                for ffile in files_2019:
                    os.chdir("D:\master concordia\DYD\Ecobee DYD\canada\Canada 2019")
                    if ffile in files_2017 and f in files_2018:
                        df_ffile= pd.read_csv(ffile)
                        df_total= pd.concat([df_ffile], ignore_index=True)
                        df_total.to_csv(("thermostat"+str(i)+".csv"),(output_folder))
                        i +=1

我正试图写一个代码来组合5个excel文件的名称相同，但在不同的文件夹，这是我到目前为止得到的问题是它只读取第一个文件，有人能告诉我如何修复它吗？你知道吗