Rename only first 4 characters of filename

[bmatt8]

Im trying to rename only the first 4 characters of a filename.

Example: rename a045av18.c00 to paav18.c00

The "av18" will change each day so i just want to replace "a045" with "pa" and thats it.

Having a hard time getting this to work. I tried a rename with DOS commands but it doesnt work with a wildcard.

import os
import sys
import re

if __name__ == "__main__":
    _, indir = sys.argv

    infiles = [f for f in os.listdir(indir) if os.path.isfile(os.path.join(indir

    for infile in infiles:
        outfile = re.sub(r'pa', r'a045' , infile)
        os.rename(os.path.join(indir, infile), os.path.join(indir, outfile))