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As software applications grow in size and complexity, maintaining all code within a single file becomes inefficient and error-prone.

Challenges of Single-File Programs

Solution: Modular Programming

To address these issues, Python encourages modular programming, where:

What Is a Module?

A module is a Python file (.py) that contains:

Each module represents a logical unit of functionality, such as calculations, user management, or database operations.

calc.py

def add():
    return "addition"

def sub():
    return "subtraction"

Python does not automatically search for functions in other files to avoid naming conflicts. You must explicitly import what you need.

import calc

result = calc.add()
print(result)

Output:

addition

Instead of importing the whole module, you can import only what you need.

from calc import sub

result = sub()
print(result)

Output:

subtraction

You can also import multiple functions:

from calc import add, sub

print(add())
print(sub())

Python allows importing everything from a module using *.

from calc import *

print(add())
print(sub())

⚠ Note: Wildcard imports are generally discouraged in large projects because they can:

A package is a folder (directory) that contains:

Packages help organize large applications by grouping related functionality.

calculator/
│
├── calc.py
└── demo.py

Packages_in_Python

When a Python file is outside the package, you must use the package name + module name.

from calculator.calc import add

result = add()
print(result)

Output:

addition

This avoids ambiguity and clearly defines where the function is coming from.

Modules are single Python files containing reusable code.
Packages are folders containing related modules.
Python requires explicit imports to avoid confusion.
You can import:
- Entire modules
- Specific functions
- All functions (with caution)
Modules and packages are essential for large-scale Python development.

Written By: Muskan Garg