Reading Other People's Code Competent¶

The systematic approach¶

The systematic approach — a key concept in Reading Other People's Code.

1. Start from the entry point¶

What runs first?
├── main.py / __main__.py
├── app = FastAPI() → which routes?
├── if __name__ == "__main__" → what's called?
└── CLI entry point (pyproject.toml scripts)

2. Read tests first¶

Tests tell you: - What the code is supposed to do - What inputs/outputs look like - Edge cases the author considered - How to use the API

3. Map the architecture¶

┌── Read folder structure (what's the organization?)
├── Read imports (what depends on what?)
├── Find the domain objects (models, entities)
├── Find the entry points (routes, CLI, jobs)
└── Find the data flow (input → process → output)

4. Use tools¶

# Find where something is defined
grep -rn "class UserService" src/

# Find all usages of a function
grep -rn "create_user" src/

# Understand dependencies
pip show package_name   # what it does
pipdeptree              # dependency tree

# Generate call graph
pyan3 src/**/*.py --dot | dot -Tpng -o callgraph.png

Strategies for different situations¶

Strategies for different situations in Reading Other People's Code — what it is and when to use it.

Practice Exercises¶

1. Clone a popular library (requests, click, flask) and trace a simple operation through the code.
2. Read a PR on a project you use — understand the change without context.
3. Map the architecture of a Django/FastAPI project by only reading file structure and imports.
4. Add a feature to an unfamiliar open-source project (start with "good first issue" labels).