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🔧 Intermediate

Python Packages – Organising Code into Directories

A package is a directory containing Python modules and a special __init__.py file. Packages let you organise large codebases into logical namespaces and are how third-party libraries like NumPy, Pandas, and Flask are distributed.

⏱️ 18 min read🎯 Intermediate📅 Updated 2026

Package Structure

A package is just a directory with __init__.py. Sub-packages are nested directories, each with their own __init__.py.

Python
# Project structure:
# myproject/
#   __init__.py
#   math_utils.py
#   string_utils.py
#   data/
#       __init__.py
#       loader.py

# Importing from the package:
from myproject import math_utils
from myproject.data import loader
from myproject.string_utils import clean_text

The __init__.py File

__init__.py runs when the package is imported. Use it to expose the package's public API.

Python
# myproject/__init__.py
from .math_utils import add, subtract
from .string_utils import clean_text

__version__ = "1.0.0"
__all__ = ["add", "subtract", "clean_text"]

# Now users can do:
# from myproject import add  (instead of myproject.math_utils.add)

Installing Third-Party Packages with pip

pip is Python's package manager. Install packages from PyPI (Python Package Index).

Python
# Install a package
# pip install requests

# Install specific version
# pip install requests==2.31.0

# Install from requirements file
# pip install -r requirements.txt

# List installed packages
# pip list

# Save current environment to file
# pip freeze > requirements.txt
💡
Tip

Always use a virtual environment before pip installing packages for a project.

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requirements.txt – Reproducible Environments

Share your project's dependencies so others can install exactly the same versions.

Python
# requirements.txt
requests==2.31.0
flask==3.0.0
pandas>=2.0.0
numpy>=1.24.0
python-dotenv==1.0.0

# Install all at once:
# pip install -r requirements.txt

Relative vs Absolute Imports

Inside a package, use relative imports (dot notation) to reference sibling modules.

Python
# Inside myproject/math_utils.py:
from . import string_utils          # Sibling module
from .data.loader import read_csv   # Sub-package
from myproject.config import DEBUG  # Absolute import
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