ProvRecord.get_attribute behaviour differs from its doc string

[cdboer]

class ProvRecord(object):
    def __init__(self, bundle, identifier, attributes=None):
        ...
        self._attributes = defaultdict(set)
        ...

    def get_attribute(self, attr_name):
        """
        Returns the attribute of the given name.
        :param attr_name: Name of the attribute.
        :return: Tuple (name, value)
        """
        attr_name = self._bundle.valid_qualified_name(attr_name)
        return self._attributes[attr_name]

The doc string implies, that get_attribute returns a tuple containing the attribute name aswell as its value.
In practice get_attribute always returns a set. Is this intended behaviour?

I was searching for a method that would return the attribute tuple or its value for a given attribute name.
I did not expect to retrieve a set.