python - 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 it would work but it does not. I would be thankful for any guidance to find my mistake.

   import os,sys
   folder = 'E:/.../1936342-G/test'
   for filename in os.listdir(folder):
           infilename = os.path.join(folder,filename)
           if not os.path.isfile(infilename): continue
           oldbase = os.path.splitext(filename)
           infile= open(infilename, 'r')
           newname = infilename.replace('.grf', '.las')
           output = os.rename(infilename, newname)
           outfile = open(output,'w')

Answer 1

The open on the source file is unnecessary, since os.rename only needs the source and destination paths to get the job done. Moreover, os.rename always returns None, so it doesn't make sense to call open on its return value.

import os
import sys
folder = 'E:/.../1936342-G/test'
for filename in os.listdir(folder):
    infilename = os.path.join(folder,filename)
    if not os.path.isfile(infilename): continue
    oldbase = os.path.splitext(filename)
    newname = infilename.replace('.grf', '.las')
    output = os.rename(infilename, newname)

I simply removed the two open. Check if this works for you.