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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 addPolicyURI(self, policy_uri):
 """Add an acceptable authentication policy URI to this request This method is intended to be used by the relying party to add acceptable authentication types to the request. @param policy_uri: The identifier for the preferred type of authentication. @see: http://openid.net/specs/openid-provider-authentication-policy-extension-1_0-01.html#auth_policies """

        if policy_uri not in self.preferred_auth_policies:
            self.preferred_auth_policies.append(policy_uri)