def list_local_devices
      local_name = "job:localhost"
      TensorStream::Evaluator.evaluators.collect { |k, v|
        v[:class].query_supported_devices.collect do |device_str|
          [local_name, "ts:#{k}:#{device_str.name}"].join("/")
        end
      }.flatten
    end
def list_local_devices
      local_name = "job:localhost"
      TensorStream::Evaluator.evaluators.collect { |k, v|
        v[:class].query_supported_devices.collect do |device_str|
          [local_name, "ts:#{k}:#{device_str.name}"].join("/")
        end
      }.flatten
    end
List available evaluators + devices in the current local environment
 Returns:
 - An array containing the names of those devices