code: def pull_buildpack(url):
      
      defrag = _defrag(urllib.parse.urldefrag(url))
      with lock_or_wait(defrag.url):
          bp = update_buildpack(url)
          dest = bp.basename + '-' + hash_text(defrag.url)
          shutil.copytree(bp.folder, dest)
      # Make the buildpack dir writable, per
      # https://bitbucket.org/yougov/velociraptor/issues/178
      path.Path(dest).chmod('a+wx')
      return dest
docs: Update a buildpack in its shared location, then make a copy into the
      current directory, using an md5 of the url.