Unique iterator for Python.

unique.py

def identity(x):
    return x


class unique(object):
    def __init__(self, xs, predicate=identity):
        """ :type xs: Iterable """
        self._xs = xs
        self._predicate = predicate

    def __iter__(self):
        """ :rtype: Iterable """
        p = self._predicate
        s = set()
        for x in self._xs:
            p_x = p(x)
            if p_x not in s:
                s.add(p_x)
                yield x