Python Modules and Package

1. Package

A package is a directory (folder) that contains an __init__.py file.

The __init__.py tells Python:
“This folder is a Python package, so you can import from it.”

Example:

myapp/
├── __init__.py
├── helpers.py

myapp is now a package.

You can import like this:

from myapp import helpers

Key idea:

A package lets you group related modules into one namespace.

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2. Module

A module is just a single Python file (.py) that contains Python code.

You can import it and use its variables, functions, classes, etc.

Example:

# utils.py (This is a Python module)

def greet(name):
    return f"Hello, {name}"

You can import this in another file:

import utils

print(utils.greet("Alice"))

Key idea:

Any .py file is a module.

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3. Subpackages and Submodules

• Packages inside packages ⇒ Subpackages
• Modules inside subpackages ⇒ Submodules

Example structure:

myapp/
├── __init__.py
├── api/  → is a subpackage
│   ├── __init__.py
│   ├── users.py  → is a submodule
│   └── items.py
├── core.py

Key idea:

Subpackages allow you to organize large codebases into smaller logical units.

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Why so many __init__.py files?

The __init__.py file marks a directory as a package or subpackage.
Without it, Python won’t treat the folder as importable.