Introduction to Modules

Functions organise a task within a program. Modules extend that organisation across files, allowing related definitions to be kept together and used elsewhere.

As programs grow, it becomes inefficient to keep all the code in one file. Python solves this with modules—separate files that organize reusable code. A module can contain functions, variables, and even entire classes, making your projects cleaner and easier to manage.

Some modules come with Python’s standard library, such as math and datetime; others are files you write or packages you install. Once imported, the functions inside a module can be used anywhere in your program.

Creating and Importing a Module

You can create your own module by saving a Python file (for example,helper.py) with some functions inside it.

# helper.py
def greet(name):
    return f"Hello, {name}! Welcome to Python."

Save the first listing as helper.py. Put the following code in main.py in the same folder and run main.py; the file named helper.py supplies the imported module:

import helper
print(helper.greet("Alice"))

Output

Hello, Alice! Welcome to Python.

This example is deterministic: the same name produces the same greeting.

You can also import specific items:

from helper import greet
print(greet("Bob"))

Output

Hello, Bob! Welcome to Python.

Or use an alias:

import helper as h
print(h.greet("Ada"))

Output

Hello, Ada! Welcome to Python.