'Update the set, removing any elements from other which are not
in both sets.
@param other: the collection of items with which to update the set
@type other: Set object'

def intersection_update(self, other):

    if (not isinstance(other, Set)):
        raise ValueError('other    must    be    a    Set    instance')
    if (self is other):
        return
    for item in list(self.items):
        if (item not in other.items):
            self.items.remove(item)
