Python Understanding Python File Extensions and Project Layouts

Python project files use extensions to indicate their purpose. Understanding the main ones will prevent common editing and execution mistakes.

Understanding the Concept

A .py file holds Python source. A .ipynb file is a Jupyter notebook. A .pyi file is a type stub that describes interfaces for type-checking tools. A project might also include .txt data, .json configuration, or a pyproject.toml file containing project metadata. Files named __init__.py have a special role in ordinary Python packages, which you will learn later. The existence of a file extension does not make its contents valid.

When and Why You Would Use This

Start with a simple folder containing main.py and perhaps a data directory. Add more folders only when needed. Do not mix your virtual environment internals with source code.

Practical Example

my_project/
    main.py
    data/
        sample.txt
    pyproject.toml  # Optional project metadata

Understanding the Example

This is a sample directory tree rather than executable code. The project entry point for a tiny program might be main.py. A real application can have many modules and packages instead.

Try It Yourself

Create main.py and a data directory. Identify which files you would write yourself and which might be generated by tooling.

Common Beginner Mistakes

• Renaming a text file from .txt to .py and assuming this fixes invalid Python syntax.
• Editing bytecode cache files instead of original Python source.
• Placing every file in the same directory after the project grows.

Key Takeaways

• Use .py for Python source and .ipynb for notebooks.
• Project layout should reflect the work being organized.
• Extensions help tools identify content but do not validate it.