For .tlt model or .trt engine, end user can run with default tlt detectnet_v2 inference to do inference.
For .etlt model, end user can deploy it with deepstream.
For .trt engine, if you try to run with your own python code, you can refer to Developer Guide :: NVIDIA Deep Learning TensorRT Documentation , mentioned in Inferring resnet18 classification etlt model with python - #12 by Morganh