How to use the tuf.repository_tool.import_rsa_privatekey_from_file function in tuf

keyid = key_object['keyid']
    self.assertEqual([keyid], self.metadata.signing_keys)

    self.metadata.unload_signing_key(key_object)

    self.assertEqual(self.metadata.signing_keys, [])


    # Test improperly formatted arguments.
    self.assertRaises(tuf.FormatError, self.metadata.unload_signing_key, 3)


    # Test non-existent key argument.
    key_path = os.path.join('repository_data',
                            'keystore', 'targets_key')
    unused_key_object = repo_tool.import_rsa_privatekey_from_file(key_path,
                                                                  'password')
    
    self.assertRaises(tuf.Error, self.metadata.unload_signing_key,
                      unused_key_object)

# Import the top-level and delegated role public keys.
  role_keys['root']['public'] = \
    repo_tool.import_rsa_publickey_from_file(root_key_file+'.pub')
  role_keys['targets']['public'] = \
    repo_tool.import_ed25519_publickey_from_file(targets_key_file+'.pub')
  role_keys['snapshot']['public'] = \
    repo_tool.import_ed25519_publickey_from_file(snapshot_key_file+'.pub')
  role_keys['timestamp']['public'] = \
      repo_tool.import_ed25519_publickey_from_file(timestamp_key_file+'.pub')
  role_keys['role1']['public'] = \
      repo_tool.import_ed25519_publickey_from_file(delegation_key_file+'.pub')

  # Import the private keys of the top-level and delegated roles.
  role_keys['root']['private'] = \
    repo_tool.import_rsa_privatekey_from_file(root_key_file, 
                                              EXPECTED_KEYFILE_PASSWORD)
  role_keys['targets']['private'] = \
    repo_tool.import_ed25519_privatekey_from_file(targets_key_file,
                                              EXPECTED_KEYFILE_PASSWORD)
  role_keys['snapshot']['private'] = \
    repo_tool.import_ed25519_privatekey_from_file(snapshot_key_file,
                                              EXPECTED_KEYFILE_PASSWORD)
  role_keys['timestamp']['private'] = \
    repo_tool.import_ed25519_privatekey_from_file(timestamp_key_file,
                                              EXPECTED_KEYFILE_PASSWORD)
  role_keys['role1']['private'] = \
    repo_tool.import_ed25519_privatekey_from_file(delegation_key_file,
                                              EXPECTED_KEYFILE_PASSWORD)

  return role_keys

# Import the top-level and delegated role public keys.
  role_keys['root']['public'] = \
    repo_tool.import_rsa_publickey_from_file(root_key_file+'.pub')
  role_keys['targets']['public'] = \
    repo_tool.import_ed25519_publickey_from_file(targets_key_file+'.pub')
  role_keys['snapshot']['public'] = \
    repo_tool.import_ed25519_publickey_from_file(snapshot_key_file+'.pub')
  role_keys['timestamp']['public'] = \
      repo_tool.import_ed25519_publickey_from_file(timestamp_key_file+'.pub')
  role_keys['role1']['public'] = \
      repo_tool.import_ed25519_publickey_from_file(delegation_key_file+'.pub')

  # Import the private keys of the top-level and delegated roles.
  role_keys['root']['private'] = \
    repo_tool.import_rsa_privatekey_from_file(root_key_file,
                                              EXPECTED_KEYFILE_PASSWORD)
  role_keys['targets']['private'] = \
    repo_tool.import_ed25519_privatekey_from_file(targets_key_file,
                                              EXPECTED_KEYFILE_PASSWORD)
  role_keys['snapshot']['private'] = \
    repo_tool.import_ed25519_privatekey_from_file(snapshot_key_file,
                                              EXPECTED_KEYFILE_PASSWORD)
  role_keys['timestamp']['private'] = \
    repo_tool.import_ed25519_privatekey_from_file(timestamp_key_file,
                                              EXPECTED_KEYFILE_PASSWORD)
  role_keys['role1']['private'] = \
    repo_tool.import_ed25519_privatekey_from_file(delegation_key_file,
                                              EXPECTED_KEYFILE_PASSWORD)

  return role_keys

timestamp_privkey_path = os.path.join(keystore_directory, 'timestamp_key')
    role1_privkey_path = os.path.join(keystore_directory, 'delegation_key')
    
    root_privkey = \
      repo_tool.import_rsa_privatekey_from_file(root_privkey_path, 'password')
    targets_privkey = \
      repo_tool.import_rsa_privatekey_from_file(targets_privkey_path,
                                                'password')
    snapshot_privkey = \
      repo_tool.import_rsa_privatekey_from_file(snapshot_privkey_path,
                                                'password')
    timestamp_privkey = \
      repo_tool.import_rsa_privatekey_from_file(timestamp_privkey_path,
                                                'password')
    role1_privkey = \
      repo_tool.import_rsa_privatekey_from_file(role1_privkey_path,
                                                'password')


    # (2) Add top-level verification keys.
    repository.root.add_verification_key(root_pubkey)
    repository.targets.add_verification_key(targets_pubkey)
    repository.snapshot.add_verification_key(snapshot_pubkey)

    # Verify that repository.write() fails for insufficient threshold
    # of signatures (default threshold = 1).
    self.assertRaises(tuf.UnsignedMetadataError, repository.write) 
    
    repository.timestamp.add_verification_key(timestamp_pubkey)
    
    
    # (3) Load top-level signing keys.

public_brakes_key = repotool.import_rsa_publickey_from_file(KEYS_DIR +
      'brakes.pub')
  public_acme_key = repotool.import_rsa_publickey_from_file(KEYS_DIR +
      'acme.pub')
  public_cell_key = repotool.import_rsa_publickey_from_file(KEYS_DIR +
      'cell.pub')
  private_director_key = repotool.import_rsa_privatekey_from_file(KEYS_DIR +
      'director', password='pw')
  if not online_only:
    private_images_key = repotool.import_rsa_privatekey_from_file(
        KEYS_OFFLINE_DIR + 'images', password='pw')
    private_brakes_key = repotool.import_rsa_privatekey_from_file(
        KEYS_OFFLINE_DIR + 'brakes', password='pw')
    private_acme_key = repotool.import_rsa_privatekey_from_file(
        KEYS_OFFLINE_DIR + 'acme', password='pw')
    private_cell_key = repotool.import_rsa_privatekey_from_file(
        KEYS_OFFLINE_DIR + 'cell', password='pw')

public_images_key = repotool.import_rsa_publickey_from_file(KEYS_DIR +
      'images.pub')
  public_director_key = repotool.import_rsa_publickey_from_file(KEYS_DIR +
      'director.pub')
  public_brakes_key = repotool.import_rsa_publickey_from_file(KEYS_DIR +
      'brakes.pub')
  public_acme_key = repotool.import_rsa_publickey_from_file(KEYS_DIR +
      'acme.pub')
  public_cell_key = repotool.import_rsa_publickey_from_file(KEYS_DIR +
      'cell.pub')
  private_director_key = repotool.import_rsa_privatekey_from_file(KEYS_DIR +
      'director', password='pw')
  if not online_only:
    private_images_key = repotool.import_rsa_privatekey_from_file(
        KEYS_OFFLINE_DIR + 'images', password='pw')
    private_brakes_key = repotool.import_rsa_privatekey_from_file(
        KEYS_OFFLINE_DIR + 'brakes', password='pw')
    private_acme_key = repotool.import_rsa_privatekey_from_file(
        KEYS_OFFLINE_DIR + 'acme', password='pw')
    private_cell_key = repotool.import_rsa_privatekey_from_file(
        KEYS_OFFLINE_DIR + 'cell', password='pw')

# Import public and private keys from the generated files.
  public_root_key = repotool.import_rsa_publickey_from_file(KEYS_DIR +
      'root.pub')
  public_time_key = repotool.import_rsa_publickey_from_file(KEYS_DIR +
      'time.pub')
  public_snap_key = repotool.import_rsa_publickey_from_file(KEYS_DIR +
      'snap.pub')
  public_targets_key = repotool.import_rsa_publickey_from_file(KEYS_DIR +
      'targets.pub')
  private_time_key = repotool.import_rsa_privatekey_from_file(KEYS_DIR +
      'time', password='pw')
  private_snap_key = repotool.import_rsa_privatekey_from_file(KEYS_DIR +
      'snap', password='pw')
  if not online_only:
    private_root_key = repotool.import_rsa_privatekey_from_file(
        KEYS_OFFLINE_DIR + 'root', password='pw')
    private_targets_key = repotool.import_rsa_privatekey_from_file(
        KEYS_OFFLINE_DIR + 'targets', password='pw')

  # Import delegated keys.
  public_images_key = repotool.import_rsa_publickey_from_file(KEYS_DIR +
      'images.pub')
  public_director_key = repotool.import_rsa_publickey_from_file(KEYS_DIR +
      'director.pub')
  public_brakes_key = repotool.import_rsa_publickey_from_file(KEYS_DIR +
      'brakes.pub')
  public_acme_key = repotool.import_rsa_publickey_from_file(KEYS_DIR +
      'acme.pub')
  public_cell_key = repotool.import_rsa_publickey_from_file(KEYS_DIR +
      'cell.pub')
  private_director_key = repotool.import_rsa_privatekey_from_file(KEYS_DIR +