Change the file extension for files in a folder?

Question

I would like to change the extension of the files in specific folder. i read about this topic in the forum. using does ideas, I have written following code and I expect that

Answer 1

import os

dir =("C:\\Users\\jmathpal\\Desktop\\Jupyter\\Arista")
for i in os.listdir(dir):
    files = os.path.join(dir,i)
    split= os.path.splitext(files)
    if split[1]=='.txt':
       os.rename(files,split[0]+'.csv')