TorchScript export in PyTorch - ML Experiment: Train & Evaluate

Experiment - TorchScript export

Problem:You have a PyTorch model trained for image classification. You want to export it using TorchScript to run it efficiently in a production environment without Python dependency.

Current Metrics:Training accuracy: 92%, Validation accuracy: 89%, Model is trained and working in PyTorch but not exported.

Issue:The model is not exported yet. You need to convert it to TorchScript format correctly to use it outside Python.

Your Task

Export the trained PyTorch model to TorchScript format using tracing or scripting, then load and run inference with the exported model to verify it produces the same predictions.

Do not retrain the model.

Use either torch.jit.trace or torch.jit.script for export.

Verify the exported model outputs match the original model outputs on sample input.

Hint 1

Hint 2

Hint 3

Solution

PyTorch

import torch
import torch.nn as nn

# Define a simple model for demonstration
class SimpleCNN(nn.Module):
    def __init__(self):
        super(SimpleCNN, self).__init__()
        self.conv = nn.Conv2d(3, 16, 3, stride=1, padding=1)
        self.relu = nn.ReLU()
        self.pool = nn.AdaptiveAvgPool2d((1,1))
        self.fc = nn.Linear(16, 10)
    def forward(self, x):
        x = self.conv(x)
        x = self.relu(x)
        x = self.pool(x)
        x = torch.flatten(x, 1)
        x = self.fc(x)
        return x

# Assume model is trained
model = SimpleCNN()
model.eval()

# Sample input for tracing
example_input = torch.randn(1, 3, 32, 32)

# Export model using tracing
traced_model = torch.jit.trace(model, example_input)

# Save the traced model
traced_model.save("traced_model.pt")

# Load the traced model
loaded_model = torch.jit.load("traced_model.pt")
loaded_model.eval()

# Verify outputs match
with torch.no_grad():
    original_output = model(example_input)
    traced_output = loaded_model(example_input)

# Check if outputs are close
outputs_match = torch.allclose(original_output, traced_output, atol=1e-6)

print(f"Outputs match: {outputs_match}")

Changed super().__init__() to super(SimpleCNN, self).__init__() for compatibility.

Results Interpretation

Before export: Model runs only in PyTorch with Python dependency.

After export: Model runs as TorchScript module, outputs match original model exactly.

TorchScript export allows running PyTorch models efficiently outside Python while preserving model behavior.

Bonus Experiment

Try exporting the same model using torch.jit.script instead of tracing and compare the results.

💡 Hint

Use torch.jit.script(model) and verify outputs similarly.

Practice

1. What is the main purpose of exporting a PyTorch model using TorchScript?

easy

A. To increase the training speed of the model

B. To save the model so it can run independently without Python

C. To convert the model into a TensorFlow format

D. To visualize the model architecture

Solution

1. Step 1: Understand TorchScript export purpose

   TorchScript export saves PyTorch models in a format that can run without Python, making deployment easier.

2. Step 2: Compare options with purpose

   Only To save the model so it can run independently without Python correctly states the main purpose: saving for standalone use without Python.

3. Final Answer:

   To save the model so it can run independently without Python -> Option B

4. Quick Check:

   TorchScript export = standalone model saving [OK]

Hint: TorchScript export = run model without Python [OK]

Common Mistakes:

• Thinking it speeds up training
• Confusing with TensorFlow conversion
• Assuming it is for visualization

2. Which of the following is the correct way to export a PyTorch model using scripting in TorchScript?

easy

A. torch.jit.trace(model, example_input)

B. torch.load('model.pt')

C. torch.save(model.state_dict(), 'model.pt')

D. torch.jit.script(model)

Solution

1. Step 1: Identify scripting syntax

   Using scripting to export a model requires torch.jit.script(model).

2. Step 2: Differentiate from tracing and saving

   torch.jit.trace(model, example_input) is tracing, torch.save(model.state_dict(), 'model.pt') saves weights only, torch.load('model.pt') loads a model, so only torch.jit.script(model) is correct for scripting export.

3. Final Answer:

   torch.jit.script(model) -> Option D

4. Quick Check:

   Scripting export uses torch.jit.script [OK]

Hint: Scripting export uses torch.jit.script(model) [OK]

Common Mistakes:

• Confusing scripting with tracing
• Using torch.save instead of torch.jit.script
• Trying to load instead of export

3. Given the code below, what will be the output of print(traced_model(torch.tensor([2.0])))?

import torch
class SimpleModel(torch.nn.Module):
    def forward(self, x):
        return x * 3

model = SimpleModel()
example_input = torch.tensor([1.0])
traced_model = torch.jit.trace(model, example_input)
print(traced_model(torch.tensor([2.0])))

medium

A. tensor([2.0])

B. tensor([3.0])

C. tensor([6.0])

D. RuntimeError

Solution

1. Step 1: Understand model behavior

   The model multiplies input by 3, so input 2.0 becomes 6.0.

2. Step 2: Check traced model output

   Tracing records the multiply by 3 operation, so traced_model(2.0) outputs tensor([6.0]).

3. Final Answer:

   tensor([6.0]) -> Option C

4. Quick Check:

   Input 2.0 * 3 = 6.0 [OK]

Hint: Model multiplies input by 3, so output is input*3 [OK]

Common Mistakes:

• Confusing input with output
• Expecting tracing to fail
• Thinking output is unchanged input

4. What is the error in the following code snippet when exporting a model with TorchScript scripting?

import torch
class MyModel(torch.nn.Module):
    def forward(self, x):
        if x.sum() > 0:
            return x * 2
        else:
            return x - 2

model = MyModel()
scripted_model = torch.jit.trace(model, torch.tensor([1.0]))

medium

A. Using torch.jit.trace instead of torch.jit.script for model with conditions

B. Missing example input tensor

C. Model class missing __init__ method

D. Incorrect tensor datatype

Solution

1. Step 1: Identify model features

   The model has a condition (if statement) in forward, which tracing cannot capture correctly.

2. Step 2: Understand TorchScript export methods

   Tracing works only for simple models without control flow; scripting is needed for conditions.

3. Final Answer:

   Using torch.jit.trace instead of torch.jit.script for model with conditions -> Option A

4. Quick Check:

   Model with conditions requires scripting, not tracing [OK]

Hint: Use scripting for models with if/else, not tracing [OK]

Common Mistakes:

• Using trace on models with control flow
• Assuming missing input tensor causes error
• Thinking __init__ is mandatory here

5. You want to export a PyTorch model that uses a loop and conditional statements inside its forward method. Which approach should you use to export it with TorchScript, and why?

hard

A. Use torch.jit.script because it supports control flow like loops and conditions

B. Use torch.jit.trace because it records operations for any model

C. Use torch.save to save the model weights only

D. Use torch.jit.trace with multiple example inputs to cover all paths

Solution

1. Step 1: Analyze model features

   The model has loops and conditions, which require TorchScript to understand control flow.

2. Step 2: Choose correct export method

   torch.jit.script compiles the model including control flow, while tracing cannot handle dynamic paths.

3. Final Answer:

   Use torch.jit.script because it supports control flow like loops and conditions -> Option A

4. Quick Check:

   Loops and conditions need scripting export [OK]

Hint: Loops and conditions require torch.jit.script export [OK]

Common Mistakes:

• Using tracing for models with dynamic control flow
• Saving weights only instead of full model
• Trying to cover all paths with tracing