Learn PyTorch from Scratch: A Complete Practical Guide for Deep Learning Beginners

Core Project Information

• Project Name: pytorch-from-scratch
• Original Author: afdezcaravaca
• Source Platform: GitHub
• Link: https://github.com/afdezcaravaca/pytorch-from-scratch
• Release Date: June 3, 2026

Guide

This article introduces a PyTorch introductory project for deep learning beginners. It aims to help readers break free from the "package caller" dilemma—starting from the most basic Tensor operations, gradually understanding the essence of neural networks, training processes, and deep learning fundamentals, and building a solid theoretical foundation and practical skills. The project uses Jupyter Notebooks, allowing beginners to learn interactively by reading and practicing simultaneously to grasp the underlying principles.

Background: Why is Learning PyTorch from Scratch Important?

In today's rapidly developing AI field, PyTorch has become a popular framework in both academia and industry due to its dynamic computation graph, intuitive API, and strong community support. However, many beginners only know how to call pre-built models but cannot understand the underlying principles (the "package caller" problem). This project was created to solve this issue—it does not rely on pre-packaged high-level APIs, instead explaining from the basics to help learners truly master the core logic of deep learning.

Project Structure: A Structured Learning Path

The project organizes content using Jupyter Notebooks and covers three core themes:

1. PyTorch Basics and Tensor Operations: From Tensor creation, indexing, slicing to broadcasting mechanisms and automatic differentiation—laying a solid foundation;
2. Neural Network Construction Principles: Manually implementing forward/backward propagation, activation functions, loss functions, and optimization algorithms to understand the essence of "gradient descent" and neural network "learning";
3. Complete Training Process: Connecting data loading, batch processing, training loops, validation, and testing to form a reusable training pipeline.

Core Mechanism: Analysis of Automatic Differentiation and Backpropagation

PyTorch's automatic differentiation system (Autograd) is one of its core features:

• Dynamic Computation Graph: Uses the Define-by-Run mode, where the computation graph is built in real-time during each forward pass, making debugging more intuitive (compared to TensorFlow 1.x's static graph);
• Gradient Calculation: Automatically computes partial derivatives of Tensors via the backward() method, and manually implements parameter updates to understand the essence of optimizers;
• Gradient Handling: Explains when to zero gradients and how to process batch data to avoid memory leaks and training instability.

Practical Significance: From Theory to Application

After mastering the content of this project, learners can:

• Enter the Research Field: Easily read papers and reproduce algorithms (applicable to CV, NLP, reinforcement learning, etc.);
• Develop Industrial Projects: Flexibly use high-level APIs like torch.nn/torch.optim and adjust models and training strategies according to requirements;
• Customize Innovations: When existing frameworks are insufficient, customize layers, loss functions, and optimizers to implement unique algorithms.

Learning Suggestions and Advanced Path

Learning Suggestions:

1. First read through the Notebook to understand the overall idea, then run the code line by line;
2. Modify hyperparameters and network structures to observe changes in results;
3. Apply the knowledge to your own datasets and problems to complete the transition from imitation to creation.

Advanced Path: After completing this project, you can further learn tools like PyTorch Lightning and Hugging Face Transformers, or deeply explore the implementation of SOTA models in the CV/NLP fields.

Conclusion

AI technology iterates rapidly—frameworks and tools may become outdated, but underlying principles are eternal. This project helps learners build an understanding of deep learning fundamentals. Whether you are a beginner student or a developer looking to solidify your foundation, it is worth studying carefully.