Python Modules

Modules in Python are files containing Python code. They help organize code into manageable and reusable parts. Modules can contain functions, classes, variables, and runnable code. Python has a rich standard library of modules, and you can also create or install custom ones.

Types of Modules

1. Built-in Modules:

• These are already installed by Python, for example: math, os, sys, etc.
• You do not need to install them; they can be imported and used directly.

2. Standard Library Modules:

• Python offers a rich variety of modules that can accomplish most of the tasks involved, such as datetime, random, json, etc.

3. External Modules:

• Those are third-party modules. These modules are not within the reach of the standard library, examples including numpy, pandas, etc.
• These need to be installed with the help of an external package manager like pip.

4. User-defined Modules:

• These are modules that you develop to structure your personal code.

Using a Module

Importing a Module

You can import a module using the import statement.

# Example: Importing the math module
import math
print(math.sqrt(16)) # Outputs 4.0

Importing Specific Items

You can import specific functions, classes, or variables.

from math import sqrt, pi
print(sqrt(25)) # Outputs 5.0
print(pi) # Outputs 3.141592653589793

Aliasing Modules

Use the as keyword to assign an alias.

import math as m
print(m.sqrt(9)) # Outputs 3.0

Importing All Items

This imports everything from a module but is generally discouraged due to potential name conflicts.

from math import *
print(sin(0)) # Outputs 0.0

Creating a User-Defined Module

1. Create a Python file with a .py extension.
2. Define functions, variables, or classes in it.

Example: Create a module named my_module.py

# my_module.py
def greet(name):
   return f"Hello, {name}!"

pi = 3.14159

Using the module in another file:

import my_module
print(my_module.greet("Alice")) # Outputs "Hello, Alice!"
print(my_module.pi) # Outputs 3.14159

Module Search Path

When you import a module, Python searches for it in the following order:

1. Built-in modules, such as math.
2. Directories in the sys.path variable, including:
   • The directory of the current script.
   • Directories listed in environment variables such as PYTHONPATH.
   • Standard library directories.

Example: Checking the search path

import sys
print(sys.path)

Packages: Modules Organized in Directories

A package is a collection of related modules grouped into a directory. It must contain an __init__.py file (can be empty).

Example: Package structure

mypackage/
   init.py
   module1.py
   module2.py

Using the package:

from mypackage import module1

Popular Built-in Modules

1. os: Interact with the operating system.

import os
print(os.getcwd()) # Get current working directory

2. sys: Access Python runtime information.

import sys
print(sys.version) # Python version

3. math: Perform mathematical operations.

import math
print(math.factorial(5)) # Outputs 120

4. datetime: Handle dates and times.

from datetime import datetime
print(datetime.now()) # Current date and time

5. random: Generate random numbers.

import random
print(random.randint(1, 10)) # Random integer between 1 and 10

Best Practices for Using Modules

1. Use descriptive names for your custom modules to avoid conflicts.
2. Do not import module * unless really needed.
3. Focus the modules on having a single responsibility.
4. Use virtual environments for external modules to avoid dependency conflicts.