docs: def listIDs(basedir):
      """Lists digital object identifiers of Pairtree directory structure.
  
      Walks a Pairtree directory structure to get IDs. Prepends prefix
      found in pairtree_prefix file. Outputs to standard output.
      """
      prefix = ''
      # check for pairtree_prefix file
      prefixfile = os.path.join(basedir, 'pairtree_prefix')
      if os.path.isfile(prefixfile):
          rff = open(prefixfile, 'r')
          prefix = rff.readline().strip()
          rff.close()
      # check for pairtree_root dir
      root = os.path.join(basedir, 'pairtree_root')
      if os.path.isdir(root):
          objects = pairtree.findObjects(root)
          for obj in objects:
              doi = os.path.split(obj)[1]
              # print with prefix and original chars in place
              print(prefix + pairtree.deSanitizeString(doi))
      else:
          print('pairtree_root directory not found')