n00b help with referencing files

[theturd]

This is my current code.  So the refFile will be in /some/dir/path(A-Z)/file.  The filethatneedsmodified will be in /some/other/dir/path(A-Z)/filethatneedsmodified.  I'm not sure how to iterate or loop over these dirs, and creating individual scripts for each file\dir obviously isn't the best way to do it.  Can I use os.path.join or something to define the two paths since both file names will remain the same across the different directories?

import fileinput
import sys

def insert_to_line(f_name):
  for line in fileinput.input(f_name, inplace=True):
      if any(item in line for item in theList) and not line.lstrip().startswith('#'):
          sys.stdout.write('# {}'.format(line))
      else:
          sys.stdout.write(line)

if __name__ == '__main__':
  with open("/some/dir/path/file", 'r') as refFile:
   theList = refFile.read().splitlines()
   f_name = "/some/other/dir/path/filethatneedsmodified"
   insert_to_line(f_name)