docs: def ListAttrs(cls):
    """A compatibility wrapper for listing class attributes.
  
    This method solves similar Python 2 compatibility issues for `dir` function as
    `GetName` does for `__name__` invocations. See documentation for `GetName` for
    more details.
  
    Once support for Python 2 is dropped all invocations of this function should
    be replaced with ordinary `dir` calls.
  
    Args:
      cls: A class object to list the attributes for.
  
    Returns:
      A list of attribute names as unicode strings.
    """
    precondition.AssertType(cls, type)
  
    if PY2:
      # TODO(user): once https://github.com/google/pytype/issues/127 is fixed,
      # pytype should be able to tell that this line is unreachable in py3.
      return [item.decode("ascii") for item in dir(cls)]  # pytype: disable=attribute-error
    else:
      return dir(cls)