rename.py

import os
import sys
from glob import glob

input = sys.argv[1]

os.chdir(input)
tiffs = glob('*.tiff')

for i in tiffs:
    filename = i
    # create new variable which trims the first 18 characters.
    filename_fix = filename[18:] 
    print filename_fix
    fix_with = 'ab595_ifard2016104'
    new_filename = fix_with + filename_fix
    print new_filename
    os.rename(filename, new_filename)