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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 request_seen(self, request):
 """Returns True if request was already seen. Parameters request : scrapy.http.Request Returns ------- bool """

        fp = self.request_fingerprint(request)
        # This returns the number of values added, zero if already exists.
        added = self.server.sadd(self.key, fp)
        return added == 0