Modules in Python

Unit 3 - 3.2 Modules in Python

Modules in Python: A Detailed Overview

In Python, a module is a file containing Python code that defines functions, classes, and variables, making it reusable across different programs. Modules help in organizing code logically and efficiently.

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1. Types of Modules in Python

Python modules can be classified into three main types:

1. Built-in Modules – Pre-installed modules that come with Python (e.g., math, sys, os).
2. User-defined Modules – Custom modules created by users to organize their code.
3. Third-party Modules – External modules installed via pip (e.g., numpy, pandas).

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2. Creating and Using a Module

A module in Python is simply a .py file containing functions, classes, and variables.

To create a Python module, write the desired code and save that in a file with .py extension. Let’s understand it better with an example:

Creating a Simple Module

Let's create a module named mymodule.py:

# mymodule.py

def add(a, b):
    return a + b

def subtract(a, b):
    return a - b

Importing a Module

To use mymodule.py in another Python script, you can import it using the import statement:

import mymodule

result = mymodule.add(5, 3)
print(result)  # Output: 8

Using from Keyword

You can import specific functions from a module:

from mymodule import add

print(add(10, 4))  # Output: 14

Using as Keyword for Aliasing

You can rename a module while importing:

import mymodule as mm

print(mm.subtract(10, 5))  # Output: 5

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3. Built-in Modules in Python

Python has several built-in modules. Here are a few common ones:

a) math Module – Provides mathematical functions.

import math

print(math.sqrt(16))   # Output: 4.0
print(math.factorial(5))  # Output: 120

b) random Module – Used for generating random numbers.

import random

print(random.randint(1, 100))  # Output: Random number between 1 and 100

c) datetime Module – Handles date and time.

import datetime

current_time = datetime.datetime.now()
print(current_time)

d) os Module – Interacts with the operating system.

import os

print(os.getcwd())  # Output: Current working directory

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4. Installing and Using Third-party Modules

Python allows installation of external modules via pip (Python's package manager).

Installing a Module

pip install numpy

Using the Installed Module

import numpy as np

arr = np.array([1, 2, 3])
print(arr)  # Output: [1 2 3]

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5. Special Module Attributes

Python provides special attributes for modules:

# Inside mymodule.py
print(__name__)  # Outputs '__main__' if run directly, or 'mymodule' if imported

Checking if a Module is Run Directly

if __name__ == "__main__":
    print("This script is being run directly")

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6. Finding and Listing Module Functions

You can use the dir() function to list all available functions in a module:

import math
print(dir(math))  # Lists all functions in math module

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7. Python Packages (Modules Inside Folders)

A package is a collection of modules stored in a directory containing an __init__.py file.

Creating a Package

mypackage/
│── __init__.py
│── module1.py
│── module2.py

Using a Package

from mypackage import module1

module1.some_function()

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Conclusion

• Modules help in reusability and better organization of Python code.
• Built-in modules provide essential functionalities.
• User-defined modules can be created for custom functions.
• Third-party modules can be installed via pip for additional features.
• Packages organize multiple modules into structured directories.