Copies submission from Google Cloud Storage to local directory.

    Args:
      cloud_path: path of the submission in Google Cloud Storage

    Returns:
      name of the local file where submission is copied to

def copy_submission_locally(self, cloud_path):
    """Copies submission from Google Cloud Storage to local directory.

    Args:
      cloud_path: path of the submission in Google Cloud Storage

    Returns:
      name of the local file where submission is copied to
    """
    local_path = os.path.join(self.download_dir, os.path.basename(cloud_path))
    cmd = ['gsutil', 'cp', cloud_path, local_path]
    if subprocess.call(cmd) != 0:
      logging.error('Can\'t copy submission locally')
      return None
    return local_path