EasyExperience level: 0-2 years · 3-5 years1 min read

What are modules and packages, and how does import work?

Reviewed by Gurusankar M.

Asked inInfosysTCSWiproCognizant
#module#package#import#__name__#__init__.py
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Short Answer

A module is a single .py file; a package is a folder of modules (traditionally with __init__.py). `import` runs the module once and caches it in sys.modules, so re-imports are cheap. Use `if __name__ == '__main__':` to separate 'run as script' code from 'imported as a module' code.

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Concept Made Simple

Coffee Chat Question

“What are modules and packages, and how does import work?”

Remember It Faster

Mind Map Answer

Module
one .py file
Package
folder of modules (__init__.py)
import
runs once, cached in sys.modules
__name__
'__main__' when run directly

Learn by Doing

Hands-on Keyboard

python
# mymath.py
def add(a, b):
    return a + b

if __name__ == "__main__":
    print(add(2, 3))     # only when run directly

# other.py
from mymath import add
print(add(10, 5))        # import doesn't run the __main__ block
Output
15

Think Beyond the Expected

What If?

What is the point of `if __name__ == '__main__':`?

It lets a file work both as a runnable script and an importable module. When run directly, __name__ is '__main__' and the block executes; when imported, __name__ is the module name, so that block is skipped — preventing your test/CLI code from firing on import.

Real World

Every project is organized into modules/packages; the `__main__` guard is why importing a utility file doesn't accidentally run its demo code — a detail interviewers check that beginners often miss.

Interviewer's Expectation

Keywords they're listening for:

  • module=file, package=folder
  • import runs once & caches
  • __name__=='__main__' guard
  • absolute vs relative imports

Common Mistakes

  • Naming a file the same as a stdlib module (shadowing)
  • Wildcard `from x import *`
  • Creating circular imports

Best Practices

  • Guard script code with `if __name__ == '__main__'`
  • Prefer explicit imports over `import *`
  • Keep packages cohesive; avoid circular deps

Follow-up Questions

  1. Absolute vs relative imports?
  2. What causes a circular import and how do you fix it?
  3. How does Python find modules (sys.path)?

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Plain-language foundations

I'm preparing for a software engineering interview and want to understand this from scratch, as a beginner.

Topic: Modules (Python)
Interview question: "What are modules and packages, and how does import work?"

Please:
1. Explain the core idea in simple, plain language, using an everyday analogy.
2. Define any technical terms you use.
3. Walk through one small, concrete example.
4. Finish with a single sentence I can easily remember.

Keep the tone friendly and assume I'm new to this topic.
Open inChatGPTGeminiClaude

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