Importing Modules in Python (Built-in & Custom Modules)

What is a Module in Python?

A module is a Python file (.py) that contains reusable functions, classes, or variables. Python provides two main types of modules:

  • Built-in modules (e.g., math, os, random)
  • Custom/user-defined modules (your own .py files)


How to Import Modules in Python

Python provides multiple ways to import modules:

Standard Import

import math
print(math.sqrt(16))  # Output: 4.0

Import Specific Items

from math import pi, pow
print(pi)          # Output: 3.141592653589793
print(pow(2, 3))   # Output: 8.0

Import with Alias

import random as rnd
print(rnd.randint(1, 10))


Built-in Modules in Python

Python has a rich set of built-in modules you can use without installing anything.

Module Purpose Example Function
math Math operations sqrt(), pow()
os Operating system tasks os.getcwd()
sys Python runtime interaction sys.argv
random Random number generation randint(), choice()
datetime Date & time handling datetime.now()

Example: Using os Module

import os

print("Current Directory:", os.getcwd())

Output:

Current Directory: /your/path/


Custom/User-Defined Modules

You can create your own module by simply writing Python code in a .py file.

Step-by-Step Example

Step 1: Create a file named mymodule.py

# mymodule.py
def welcome(name):
    return f"Welcome, {name}!"

PI = 3.14159

Step 2: Import the module in another file

# main.py
import mymodule

print(mymodule.welcome("Alice"))
print(mymodule.PI)

Output:

Welcome, Alice!
3.14159

Python Import Variations

Syntax Description
import module Imports entire module
from module import name Imports specific item
from module import * Imports everything (not recommended)
import module as alias Imports with alias

Importing from Packages (Custom or Installed)

from mypackage.utils import helper_function

You must ensure that:

  • The package folder has an __init__.py file
  • The structure is correct

Handling Import Errors

If you see ModuleNotFoundError:

  • Make sure the module is in the same directory or Python path
  • Check spelling and file names
  • Ensure __init__.py exists in packages (for legacy compatibility)