code: def _expires_in(self):
          
          if self.token_expiry:
              now = _UTCNOW()
              if self.token_expiry > now:
                  time_delta = self.token_expiry - now
                  # TODO(orestica): return time_delta.total_seconds()
                  # once dropping support for Python 2.6
                  return time_delta.days * 86400 + time_delta.seconds
              else:
                  return 0
docs: Return the number of seconds until this token expires.
  
          If token_expiry is in the past, this method will return 0, meaning the
          token has already expired.
  
          If token_expiry is None, this method will return None. Note that
          returning 0 in such a case would not be fair: the token may still be
          valid; we just don't know anything about it.