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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_instance_configs(self, page_size=None, page_token=None):
 """List available instance configurations for the client's project. .. _RPC docs: https://cloud.google.com/spanner/docs/reference/rpc/\ google.spanner.admin.instance.v1#google.spanner.admin.\ instance.v1.InstanceAdmin.ListInstanceConfigs See `RPC docs`_. :type page_size: int :param page_size: Optional. The maximum number of configs in each page of results from this request. Non-positive values are ignored. Defaults to a sensible value set by the API. :type page_token: str :param page_token: Optional. If present, return the next batch of configs, using the value, which must correspond to the ``nextPageToken`` value returned in the previous response. Deprecated: use the ``pages`` property of the returned iterator instead of manually passing the token. :rtype: :class:`~google.api_core.page_iterator.Iterator` :returns: Iterator of :class:`~google.cloud.spanner_v1.instance.InstanceConfig` resources within the client's project. """

        metadata = _metadata_with_prefix(self.project_name)
        path = "projects/%s" % (self.project,)
        page_iter = self.instance_admin_api.list_instance_configs(
            path, page_size=page_size, metadata=metadata
        )
        page_iter.next_page_token = page_token
        page_iter.item_to_value = _item_to_instance_config
        return page_iter