Python Modules & Packages

Modules

Modules are Python files containing definitions and statements. They allow you to organize your code logically and reuse code across multiple projects.

                        # Creating a module (save as mymodule.py)

                        def greet(name):

                            print(f"Hello, {name}")

                        # Importing and using the module

                        import mymodule

                        mymodule.greet("Alice") # Hello, Alice

                        # Importing specific functions

                        from mymodule import greet

                        greet("Bob") # Hello, Bob

                        # Importing with an alias

                        import mymodule as mm

                        mm.greet("Charlie") # Hello, Charlie

Python comes with many built-in modules (like math, os, sys) that you can import and use in your programs.

Packages

Packages are a way of organizing related modules into a directory hierarchy. A package is essentially a directory containing Python modules and a special __init__.py file.

                        # Directory structure for a package

                        mypackage/

                          ├── __init__.py # Required to make Python treat the directory as a package

                          ├── module1.py

                          └── module2.py

                        # Importing from a package

                        import mypackage.module1

                        from mypackage import module2

                        # __init__.py can be empty or can contain initialization code

                        print("Initializing mypackage...")

                        from .module1 import some_function # Relative import

Packages allow for hierarchical structuring of module namespaces and help avoid naming conflicts between modules.

Python Standard Library

Python comes with a rich standard library that provides modules for many common programming tasks.

                        # Common standard library modules

                        import math # Mathematical functions

                        import os # Operating system interfaces

                        import sys # System-specific parameters

                        import datetime # Date and time handling

                        import json # JSON parsing and encoding

                        import re # Regular expressions

                        import random # Random number generation

                        # Example usage

                        print(math.sqrt(16)) # 4.0

                        print(datetime.date.today()) # Current date

                        print(random.choice(['a', 'b', 'c'])) # Random choice

The standard library is one of Python's greatest strengths, providing tools for many tasks right out of the box.

Third-Party Packages

Python has a vast ecosystem of third-party packages that can be installed using pip, Python's package installer.

                        # Installing packages with pip (run in terminal)

                        pip install numpy pandas matplotlib requests

                        # Using installed packages

                        import numpy as np

                        import pandas as pd

                        import matplotlib.pyplot as plt

                        import requests

                        # Example: Create a numpy array

                        arr = np.array([1, 2, 3])

                        print(arr * 2) # [2 4 6]

                        # Example: Make an HTTP request

                        response = requests.get('https://api.github.com')

                        print(response.json())

Popular third-party packages extend Python's capabilities for data science, web development, machine learning, and more.

Virtual Environments

Virtual environments allow you to create isolated Python environments for different projects, preventing package conflicts.

                        # Creating a virtual environment (run in terminal)

                        python -m venv myenv

                        # Activating the environment

                        # On Windows:

                        myenv\Scripts\activate

                        # On macOS/Linux:

                        source myenv/bin/activate

                        # After activation, install packages normally

                        pip install flask

                        # Deactivating the environment

                        deactivate

                        # Listing installed packages

                        pip list

                        pip freeze > requirements.txt # Save to file

                        # Installing from requirements.txt

                        pip install -r requirements.txt

Virtual environments are essential for managing dependencies and ensuring project reproducibility.