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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 clean(self):
 """ Check unauthenticated user's cookie as a light check to prevent duplicate votes. """

        bits = (self.data["content_type"], self.data["object_pk"])
        request = self.request
        self.current = "%s.%s" % bits
        self.previous = request.COOKIES.get("yacms-rating", "").split(",")
        already_rated = self.current in self.previous
        if already_rated and not self.request.user.is_authenticated():
            raise forms.ValidationError(ugettext("Already rated."))
        return self.cleaned_data