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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def _page_streamable(page_descriptor):
 """Creates a function that yields an iterable to performs page-streaming. Args: page_descriptor (:class:`PageDescriptor`):
 indicates the structure of page streaming to be performed. Returns: Callable: A function that returns an iterator. """


    def inner(a_func, settings, request, **kwargs):
        """Actual page-streaming based on the settings."""
        page_iterator = gax.PageIterator(
            a_func, page_descriptor, settings.page_token, request, **kwargs)
        if settings.flatten_pages:
            return gax.ResourceIterator(page_iterator)
        else:
            return page_iterator

    return inner