code: def fast_sync_fetch(working_dir, import_url):
      
      try:
          fd, tmppath = tempfile.mkstemp(prefix='.blockstack-fast-sync-', dir=working_dir)
      except Exception, e:
          log.exception(e)
          return None
      
      log.debug("Fetch {} to {}...".format(import_url, tmppath))
  
      try:
          path, headers = urllib.urlretrieve(import_url, tmppath)
      except Exception, e:
          os.close(fd)
          log.exception(e)
          return None
      
      os.close(fd)
      return tmppath
docs: Get the data for an import snapshot.
      Store it to a temporary path
      Return the path on success
      Return None on error