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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 preview_page_version(request, revision_id):
 """ Returns GET response for specified page preview. :param request: the request instance. :param reversion_pk: the page revision ID. :rtype: django.http.HttpResponse. """

    revision = get_object_or_404(PageRevision, pk=revision_id)

    if not revision.page.permissions_for_user(request.user).can_publish():
        raise PermissionDenied

    page                = revision.as_page_object()
    request.revision_id = revision_id

    return page.serve_preview(request, page.default_preview_mode)