code: def file_exists(file_path, credentials=None):
    
    if file_path.startswith('gs://'):
      return _file_exists_in_gcs(file_path, credentials)
    else:
      return os.path.isfile(file_path)
docs: Check whether the file exists, on local disk or GCS.
  
    Args:
      file_path: The target file path; should have the 'gs://' prefix if in gcs.
      credentials: Optional credential to be used to load the file from gcs.
  
    Returns:
      True if the file's there.