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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 update_instance( self, instance, field_mask, retry=google.api_core.gapic_v1.method.DEFAULT, timeout=google.api_core.gapic_v1.method.DEFAULT, metadata=None, ):
 """ Updates an instance, and begins allocating or releasing resources as requested. The returned ``long-running operation`` can be used to track the progress of updating the instance. If the named instance does not exist, returns ``NOT_FOUND``. Immediately upon completion of this request: - For resource types for which a decrease in the instance's allocation has been requested, billing is based on the newly-requested level. Until completion of the returned operation: - Cancelling the operation sets its metadata's ``cancel_time``, and begins restoring resources to their pre-request values. The operation is guaranteed to succeed at undoing all resource changes, after which point it terminates with a ``CANCELLED`` status. - All other attempts to modify the instance are rejected. - Reading the instance via the API continues to give the pre-request resource levels. Upon completion of the returned operation: - Billing begins for all successfully-allocated resources (some types may have lower than the requested levels). - All newly-reserved resources are available for serving the instance's tables. - The instance's new resource levels are readable via the API. The returned ``long-running operation`` will have a name of the format ``<instance_name>/operations/<operation_id>`` and can be used to track the instance modification. The ``metadata`` field type is ``UpdateInstanceMetadata``. The ``response`` field type is ``Instance``, if successful. Authorization requires ``spanner.instances.update`` permission on resource ``name``. Example: Args: instance (Union[dict, ~google.cloud.spanner_admin_instance_v1.types.Instance]):
 Required. The instance to update, which must always include the instance name. Otherwise, only fields mentioned in [][google.spanner.admin.instance.v1.UpdateInstanceRequest.field\_mask] need be included. If a dict is provided, it must be of the same form as the protobuf message :class:`~google.cloud.spanner_admin_instance_v1.types.Instance` field_mask (Union[dict, ~google.cloud.spanner_admin_instance_v1.types.FieldMask]):
 Required. A mask specifying which fields in [][google.spanner.admin.instance.v1.UpdateInstanceRequest.instance] should be updated. The field mask must always be specified; this prevents any future fields in [][google.spanner.admin.instance.v1.Instance] from being erased accidentally by clients that do not know about them. If a dict is provided, it must be of the same form as the protobuf message :class:`~google.cloud.spanner_admin_instance_v1.types.FieldMask` 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.spanner_admin_instance_v1.types._OperationFuture` 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 "update_instance" not in self._inner_api_calls:
            self._inner_api_calls[
                "update_instance"
            ] = google.api_core.gapic_v1.method.wrap_method(
                self.transport.update_instance,
                default_retry=self._method_configs["UpdateInstance"].retry,
                default_timeout=self._method_configs["UpdateInstance"].timeout,
                client_info=self._client_info,
            )

        request = spanner_instance_admin_pb2.UpdateInstanceRequest(
            instance=instance, field_mask=field_mask
        )
        if metadata is None:
            metadata = []
        metadata = list(metadata)
        try:
            routing_header = [("instance.name", instance.name)]
        except AttributeError:
            pass
        else:
            routing_metadata = google.api_core.gapic_v1.routing_header.to_grpc_metadata(
                routing_header
            )
            metadata.append(routing_metadata)

        operation = self._inner_api_calls["update_instance"](
            request, retry=retry, timeout=timeout, metadata=metadata
        )
        return google.api_core.operation.from_gapic(
            operation,
            self.transport._operations_client,
            spanner_instance_admin_pb2.Instance,
            metadata_type=spanner_instance_admin_pb2.UpdateInstanceMetadata,
        )