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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 list_voices( self, language_code=None, retry=google.api_core.gapic_v1.method.DEFAULT, timeout=google.api_core.gapic_v1.method.DEFAULT, metadata=None, ):
 """ Returns a list of ``Voice`` supported for synthesis. Example: Args: language_code (str):
 Optional (but recommended) `BCP-47 <https://www.rfc-editor.org/rfc/bcp/bcp47.txt>`__ language tag. If specified, the ListVoices call will only return voices that can be used to synthesize this language\_code. E.g. when specifying "en-NZ", you will get supported "en-*" voices; when specifying "no", you will get supported "no-*" (Norwegian) and "nb-*" (Norwegian Bokmal) voices; specifying "zh" will also get supported "cmn-*" voices; specifying "zh-hk" will also get supported "yue-\*" voices. retry (Optional[google.api_core.retry.Retry]):
 A retry object used to retry requests. If ``None`` is specified, requests will not be retried. timeout (Optional[float]):
 The amount of time, in seconds, to wait for the request to complete. Note that if ``retry`` is specified, the timeout applies to each individual attempt. metadata (Optional[Sequence[Tuple[str, str]]]):
 Additional metadata that is provided to the method. Returns: A :class:`~google.cloud.texttospeech_v1beta1.types.ListVoicesResponse` instance. Raises: google.api_core.exceptions.GoogleAPICallError: If the request failed for any reason. google.api_core.exceptions.RetryError: If the request failed due to a retryable error and retry attempts failed. ValueError: If the parameters are invalid. """

        # Wrap the transport method to add retry and timeout logic.
        if "list_voices" not in self._inner_api_calls:
            self._inner_api_calls[
                "list_voices"
            ] = google.api_core.gapic_v1.method.wrap_method(
                self.transport.list_voices,
                default_retry=self._method_configs["ListVoices"].retry,
                default_timeout=self._method_configs["ListVoices"].timeout,
                client_info=self._client_info,
            )

        request = cloud_tts_pb2.ListVoicesRequest(language_code=language_code)
        return self._inner_api_calls["list_voices"](
            request, retry=retry, timeout=timeout, metadata=metadata
        )