def get_hostname(backend=None, instance=None):
  """DEPRECATED: Returns the hostname for a backend or backend instance.

  Warning: This API is deprecated and will be removed in a future
  release. Please migrate to the Modules API as soon as possible.

  Args:
    backend: The name of the backend. If None, the current backend will be used.

    instance: An optoinal instance number. If provided, the hostname will
      represent the specific instance. If absent, the hostname will represent
      the backend as a whole.

  Raises:
    InvalidBackendError
    InvalidInstanceError

  Returns:
    The hostname of the backend or backend instance.
  """
  if backend is None:
    backend = get_backend()


  if not isinstance(backend, (str, unicode)):
    raise InvalidBackendError('Invalid backend: %s' % backend)

  if not re.match('^[a-zA-Z0-9\-]+$', backend):
    raise InvalidBackendError('Invalid backend: %s' % backend)


  if instance is not None:
    try:
      instance = int(instance)
    except __HOLE__:
      raise InvalidInstanceError('instance must be an integer.')


  if _is_dev2_environment():
    return _get_dev2_hostname(backend, instance)
  elif _is_dev_environment():
    return _get_dev_hostname(backend, instance)

  hostname = app_identity.get_default_version_hostname()
  if hostname is None:
    raise DefaultHostnameError

  hostname = '%s.%s' % (backend, hostname)
  if instance is not None:
    hostname = '%d.%s' % (instance, hostname)
  return hostname
dataset/ETHPy150Open GoogleCloudPlatform/python-compat-runtime/appengine-compat/exported_appengine_sdk/google/appengine/api/backends/backends.py/get_hostname