Change the file extension for files in a folder?

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
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.

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