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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 parse_plays_stream(self):
 """Generate and yield a stream of parsed plays. Useful for per play processing."""

        
        lx_doc = self.html_doc()
        if lx_doc is not None:
            parser = PlayParser(self.game_key.season, self.game_key.game_type)
            plays = lx_doc.xpath('//tr[@class = "evenColor"]')
            for p in plays:
                p_obj = parser.build_play(p)
                self.plays.append(p_obj)
                
                yield p_obj