code: def filenames(directory, tag='', sorted=False, recursive=False):
      if recursive:
          f = [os.path.join(directory, f) for directory, _, filename in os.walk(directory) for f in filename if f.find(tag) > -1] 
      else:
          f = [os.path.join(directory, f) for f in os.listdir(directory) if f.find(tag) > -1]
      if sorted:
          f.sort()
      return f