Python Modules and Packages

What is a Module in Python?

A Python module is simply a .py file that contains Python definitions, functions, classes, or variables which can be reused in other Python programs using the import statement.




Example: Creating a Python Module

Let's say you create a file named mymodule.py:

# mymodule.py

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

PI = 3.14159

Now, in another Python file, you can use this module:

# main.py

import mymodule

print(mymodule.greet("Alice"))   # Output: Hello, Alice!
print(mymodule.PI)               # Output: 3.14159

Explanation:

  • You've just reused code via a Python module!


Types of Imports in Python

Python allows you to import modules in multiple ways:

import math
from math import sqrt
from math import pi as PI
import mymodule as mm

Import Styles:

  • import module - Full module import
  • from module import item - Direct import of specific item
  • import module as alias - Import with alias


What is a Package in Python?

A Python package is a directory that contains a collection of modules and a special __init__.py file (can be empty) that tells Python the directory is a package.



Example: Creating a Python Package

Directory structure:

myapp/
│
├── mypackage/
│   ├── __init__.py
│   ├── math_utils.py
│   └── string_utils.py
└── main.py

math_utils.py:

def add(x, y):
    return x + y

string_utils.py:

def shout(text):
    return text.upper()

main.py:

from mypackage.math_utils import add
from mypackage.string_utils import shout

print(add(5, 3))        # 8
print(shout("hello"))   # HELLO


The Role of __init__.py File

The __init__.py file marks a directory as a Python package and initializes it. It can be:

  • Empty - just marks the package
  • Functional - can import submodules or define package-level variables
# mypackage/__init__.py

from .math_utils import add

Now you can do:

from mypackage import add
print(add(2, 3))  # Output: 5


Built-in vs Custom Modules

  • Built-in: math, os, sys
  • Third-party: requests, numpy
  • User-defined: Custom .py files


Example: Using Built-in Module

import os

print(os.getcwd())         # Get current working directory
print(os.listdir("."))     # List files in current directory


Installing Third-Party Packages (Using pip)

pip install requests
import requests

response = requests.get("https://api.github.com")
print(response.status_code)  # 200


Organizing Code with Modules and Packages

  • Split logic into multiple modules for readability
  • Group related modules into packages
  • Use __init__.py to control package exposure
  • Keep your project scalable and maintainable


Absolute vs Relative Import in Python Packages

  • Absolute Import: from mypackage.module import x - For top-level clarity
  • Relative Import: from .module import x - For internal package references