def _parse(cls, scope):
    """Parses the input scope into a normalized set of strings.

    :param scope: A string or tuple containing zero or more scope names.
    :return: A set of scope name strings, or a tuple with the default scope name.
    :rtype: set
    """
    if not scope:
      return ('default',)
    if isinstance(scope, string_types):
      scope = scope.split(' ')
    scope = {str(s).lower() for s in scope if s}
    return scope or ('default',)
Parses the input scope into a normalized set of strings.

    :param scope: A string or tuple containing zero or more scope names.
    :return: A set of scope name strings, or a tuple with the default scope name.
    :rtype: set