Modules & Imports

Introduction

A module is a .py file. A package is a directory with __init__.py. import caches modules in sys.modules.

Understanding the topic

Core concepts to understand:

• import math — namespace import.
• from math import sqrt — specific import.
• Absolute vs relative imports.
• if __name__ == '__main__': for scripts.

Syntax reference

Visual flow / code:

# project/utils/math.py
def square(x): return x * x

# project/main.py
from utils.math import square
from utils import math as M

print(square(5))
print(M.square(6))

if __name__ == "__main__":
    print("Run as script")

Execution workflow

Real-world use

Modern packaging uses src/ layout + pyproject.toml. Avoid from x import * — explicit imports beat magic.

Best practices

• Prefer absolute imports.
• Never import * in production code.
• One responsibility per module.

Common mistakes

• Circular imports — split shared types into a separate module.

Hands-on exercise

Interview preparation — practice these questions:

• __name__ == '__main__' — why?
• Absolute vs relative import?
• What's sys.modules?

Summary

In summary: File = module; dir = package. Explicit imports always.