def METHOD_NAME(file_path, output_path=None, storage_client=None):
    """Copy file from GCS to local file.
     Args:
        file_path (str): The full GCS path to the file.
        output_path (str): The local file to copy to, if not set creates a
            temporary file.
        storage_client (storage.StorageClient): The Storage API Client to use
            for downloading the file using the API.
     Returns:
        str: The output_path the file was copied to.
    """
    if not storage_client:
        storage_client = storage.StorageClient({})
    if not output_path:
        tmp_file, output_path = tempfile.mkstemp()
        # Ensure the handle returned by mkstemp is not leaked.
        os.close(tmp_file)
    with open(output_path, mode='wb') as f:
        storage_client.download(full_bucket_path=file_path, output_file=f)
    return output_path