code: def file_id_to_file_name(file_id):
          
          if len(file_id) == 40 and re.match("^[a-f0-9]+$", file_id):
              return file_id
          # prefix with "re_" to avoid name collision with real fileids
          return "re_{}".format(hashlib.sha1(file_id).hexdigest())
docs: Sometimes file ids are not the file names on the device, but are instead generated
          by the API. These are not guaranteed to be valid file names so need hashing.