def __init__(self, iterable, key=lambda x: x):
        """Create a FrozenKeyedSet from iterable; key function determines uniqueness.

        `key` must be a callable taking a single argument; it is
        applied to every item in the iterable, and its result
        is used to determine set membership. That is, if key(item)
        returns the same for two items, only one of them will be
        in the set.
        The key *must* return a hashable object.
        """
        self._items = dict((key(item),item) for item in iterable)
        self._key = key
Create a FrozenKeyedSet from iterable; key function determines uniqueness.

        `key` must be a callable taking a single argument; it is
        applied to every item in the iterable, and its result
        is used to determine set membership. That is, if key(item)
        returns the same for two items, only one of them will be
        in the set.
        The key *must* return a hashable object.
        
recipes/Python/576932_Sets_custom_equalityuniqueness/recipe-576932.py