def expand(self, pcoll):
    coder = coders.registry.get_coder(pcoll)
    return (pcoll | ('CountGlobalUniqueValues' >> CombineGlobally(ApproximateUniqueCombineFn(self._sample_size, coder))))
def expand(self, pcoll):
    coder = coders.registry.get_coder(pcoll)
    return (pcoll | ('CountGlobalUniqueValues' >> CombineGlobally(ApproximateUniqueCombineFn(self._sample_size, coder))))