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This page provides examples that build model containers from models developed with PyTorch.

Each example requires the torch package be installed at a minimum. Use pip to install this in your Python environment:

PyTorch Installation Tip

NOTE: The PyTorch installation will vary slightly depending on your host machine, GPU accessibility, and preferences. Visit the PyTorch Installation Guide to ensure you are properly installing the package.

pip install torch

ResNet 50 Image Classification

This example was adapted from the torchvision guides for using pre-trained models and weights. View the torchvision documentation for reference.

Source Code

If you prefer to view the source code directly, reference this example and utility data files here.

First, install the additional dependencies required by this model.

pip install torchvision Pillow

Now, simply copy the below example code in your Python environment and editor of choice.


The below code can be used to build a model container from a torchvision pre-trained image classification model. Be sure to view the code annotations for more details.

import time
import io
import json
import torch
from PIL import Image
from typing import Mapping, Dict
from torchvision.models import resnet50, ResNet50_Weights #(1)

from chassisml import ChassisModel #(2)
from chassis.builder import DockerBuilder #(3)

# load and initialize model with the best available weights #(4)
weights = ResNet50_Weights.DEFAULT 
model = resnet50(weights=weights)
model.eval() #(5)

# define the inference transforms
preprocess = weights.transforms() #(6)

# define predict function #(7)
def predict(inputs: Mapping[str, bytes]) -> Dict[str, bytes]:

    # preprocess
    decoded =['image'])).convert("RGB")
    batch = preprocess(decoded).unsqueeze(0)

    # run inference and apply softmax
    prediction = model(batch).squeeze(0).softmax(0)

    # postprocess and format results
    _, indices = torch.sort(prediction, descending=True)
    inference_result = {
        "classPredictions": [
            {"class": weights.meta["categories"][idx.item()], "score": round(prediction[idx].item(),4)}
        for idx in indices[:5] ]

    structured_output = {
        "data": {
            "result": inference_result,
            "explanation": None,
            "drift": None,

    return {'results.json', json.dumps(structured_output).encode()}

# create chassis model object
chassis_model = ChassisModel(process_fn=predict)                        # (8)
# add metadata & requirements
chassis_model.add_requirements(["torch", "torchvision", "Pillow"])      # (9)
chassis_model.metadata.model_name = "ResNet 50 Image Classification"    # (10)
chassis_model.metadata.model_version = "0.0.1"
    accepted_media_types=["image/jpeg", "image/png"],
    description="Image to be classified by model"
    description="Classification predictions including human-readable label and the corresponding confidence score"

# test model # (11)
img_bytes = open("data/airplane.jpg", 'rb').read()
results = chassis_model.test({"image": img_bytes})

# define builder object # (12)
builder = DockerBuilder(package=chassis_model)    

# local docker mode # (13)
start_time = time.time()
res = builder.build_image(name="resnet5-image-classification", show_logs=True)
end_time = time.time()
print(f"Container image built in {round((end_time-start_time)/60, 5)} minutes")
  1. Here, we simply import the pre-trained ResNet 50 weights file and architecture
  2. Now, we will import the ChassisModel class from the Chassis SDK
  3. In addition to the ChassisModel object, we need to import a Builder object. The two available options, DockerBuilder and RemoteBuilder, will both build the same container but in different execution environments. Since we'd like to build a container locally with Docker, we will import the DockerBuilder object.
  4. Here, we will load our model using the torchvision models method and will pass the pre-trained weights as a parameter
  5. It is important to set your model to eval mode. This will turn off layers only applicable for training
  6. Our in-memory model object includes an embedded preprocessing object that we will extract into its own variable
  7. Here, we will define a single predict function, which you can think of as an inference function for your model. This function can access in-memory objects (e.g., preprocess and model), and the only requirement is it must convert input data from raw bytes form to the data type your model expects. See this guide for help on converting common data types. In this example, we process the raw bytes and convert to an image using the Pillow library, pass this processed data through to our model for predictions, and encode the output as base64-encoded JSON.
  8. Now, we will simply create a ChassisModel object directly from our predict function.
  9. With our ChassisModel object defined, there are a few optional methods we can call. Here, we will add the Python libraries our model will need to run. You can pass a list of packages you would list in a requirements.txt file that will be installed with Pip.
  10. In the next few lines, we will define the four minimum metadata fields that are required before building our container. These fields represent your model's name, version, inputs, and outputs. NOTE: There are many other optional fields you can choose to document if preferred.
  11. Before kicking off the Chassis job, we can test our ChassisModel object by passing through sample data.
  12. After our test has passed, we can prepare our model build context. To do so, we will define our builder object, which as mentioned before, will be DockerBuilder. This builder object uses your local Docker daemon to build a model container and store it on your machine.
  13. With our builder object defined with our model predict function, we can kick off the build using the DockerBuilder.build_image function to build a Docker container locally.