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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 fromSuccessResponse(cls, success_response, signed=True):
 """Construct a FetchResponse object from an OpenID library SuccessResponse object. @param success_response: A successful id_res response object @type success_response: openid.consumer.consumer.SuccessResponse @param signed: Whether non-signed args should be processsed. If True (the default), only signed arguments will be processsed. @type signed: bool @returns: A FetchResponse containing the data from the OpenID message, or None if the SuccessResponse did not contain AX extension data. @raises AXError: when the AX data cannot be parsed. """

        self = cls()
        ax_args = success_response.extensionResponse(self.ns_uri, signed)

        try:
            self.parseExtensionArgs(ax_args)
        except NotAXMessage, err:
            return None
        else:
            return self