code: def download_gcs_file(path, out_fname=None, prefix_filter=None):
    
    url = posixpath.join(GCS_BUCKET, path)
    if prefix_filter:
      url += "?prefix=%s" % prefix_filter
    stream = bool(out_fname)
    resp = requests.get(url, stream=stream)
    if not resp.ok:
      raise ValueError("GCS bucket inaccessible")
    if out_fname:
      with tf.io.gfile.GFile(out_fname, "wb") as f:
        for chunk in resp.iter_content(1024):
          f.write(chunk)
    else:
      return resp.content
docs: Download a file from GCS, optionally to a file.