Modules in Python

Introduction

As Python programs grow larger, it becomes essential to organize code into separate, reusable files. Modules are Python files that contain functions, classes, and variables which can be imported and used in other programs.

Using modules promotes code reuse, keeps programs organized, and avoids duplication. Python's standard library provides hundreds of built-in modules, and you can also create your own.

What is a Module?

A module is simply a .py file that contains Python code. Any Python file can be treated as a module. Modules can contain functions, classes, variables, and runnable code.

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

PI = 3.14159

class Calculator:
    def add(self, a, b):
        return a + b

Real-life Analogy: A module is like a toolbox. Each toolbox contains specific tools (functions, classes, variables) for a particular task. You bring the toolbox (import the module) and use its tools as needed.

Different Ways to Import Modules

Method 1: import module_name

import math
print(math.sqrt(25))      # 5.0
print(math.pi)            # 3.141592653589793
print(math.factorial(5))  # 120

Imports the entire module. Access items using module.item. Safest method, avoids naming conflicts.

Method 2: from module import item

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

Imports specific items. Use them directly without module prefix. Risk of name conflicts.

Method 3: from module import *

from math import *
print(sqrt(25))  # 5.0
print(ceil(4.3)) # 5

Imports everything. Not recommended as it pollutes the namespace.

Method 4: import module as alias

import math as m
print(m.sqrt(25))  # 5.0

Creates a shorter name. Very common: import numpy as np, import pandas as pd.

Method 5: from module import item as alias

from math import factorial as fact
print(fact(5))   # 120
print(fact(10))  # 3628800

Exploring Modules with dir() and help()

import math
print(dir(math))      # List all items in math module
help(math.sqrt)       # Detailed help for sqrt function

Module Search Path

When you import a module, Python searches in this order:

1. Current directory — where the script is running
2. PYTHONPATH — environment variable listing directories
3. Default directories — installation-dependent standard paths
4. site-packages — third-party modules installed via pip

import sys
print(sys.path)  # Shows the list of directories Python searches

pip — Package Installer for Python

pip is the standard package manager for Python. It downloads and installs packages from the Python Package Index (PyPI).

# Install a package
pip install requests

# Install a specific version
pip install requests==2.28.0

# Install multiple packages
pip install numpy pandas matplotlib

# List installed packages
pip list

# Uninstall a package
pip uninstall requests

# Save dependencies to a file
pip freeze > requirements.txt

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

Practical Examples

# Example 1: Using math module
import math

print("Square root of 144:", math.sqrt(144))
print("Power of 2^10:", math.pow(2, 10))
print("Ceiling of 4.3:", math.ceil(4.3))
print("Floor of 4.7:", math.floor(4.7))
print("Factorial of 6:", math.factorial(6))
print("Value of pi:", math.pi)

# Output:
# Square root of 144: 12.0
# Power of 2^10: 1024.0
# Ceiling of 4.3: 5
# Floor of 4.7: 4
# Factorial of 6: 720
# Value of pi: 3.141592653589793

# Example 2: Using random module
import random

print("Random float:", random.random())
print("Random int 1-10:", random.randint(1, 10))
print("Random choice:", random.choice(["a", "b", "c"]))

# Output:
# Random float: 0.7134 (varies)
# Random int 1-10: 7 (varies)
# Random choice: b (varies)

# Example 3: Creating and importing your own module
# File: myutils.py
def is_even(n):
    return n % 2 == 0

def factorial(n):
    if n <= 1:
        return 1
    return n * factorial(n - 1)

# File: main.py
from myutils import is_even, factorial

print(is_even(4))    # True
print(factorial(5))  # 120

Key Points

Common Mistakes

from math import *   # Imports everything including 'log'
log = "my variable"  # Overwrites math.log!
print(log)           # "my variable" — math.log is lost

# module_a.py imports module_b
# module_b.py imports module_a
# This creates a circular import error!

Import Methods Comparison

Practice Questions

Summary