iOS NSLog字典有的字段为什么有引号

data =     (
                {
            password = eb0b1e2b;
            pid = 8031006300;
            "play_key" = gd6e76df02wf9dgc6e8aa0eefe9g2bed;
            "SourceName_0" = "tbyg.jpg";
            "play_spid" = 31116;
            portalid = 603;
            spid = 956;
        }
    )

有引号是因为这个字符串包含了除字母和数字之外的字符，比如“_”, “.”,
参考
参考