🧩 What is __init__.py in Python?
📘 Definition
__init__.pyis a special Python file used to mark a folder as a Python package.- It tells Python: “This folder contains Python code you can import.“
📦 Where is it used?
It is placed inside a package folder like this:
mypackage/
├── __init__.py
├── add.py
├── sub.py
✅ Why __init__.py is Important
| Purpose | Explanation |
|---|---|
| Marks folder as a package | Without it, Python may not treat the folder as a package. |
| Runs code when imported | You can put code in it that runs automatically. |
| Helps in organizing imports | Makes it easy to control what’s imported. |
✅ Example 1: Simple Empty __init__.py
# __init__.py
# (can be empty)
Usage:
from mypackage import add
print(add.add(2, 3)) # Output: 5
✅ Example 2: With Code in __init__.py
# __init__.py
print("Welcome to mypackage!")
def greet():
print("Hello from the package!")
Usage:
import mypackage
mypackage.greet()
🖨 Output:
Welcome to mypackage!
Hello from the package!
✅ Example 3: Control Imports
If you want only certain modules to be accessible:
# __init__.py
__all__ = ['add']
Now:
from mypackage import *
# Only add is available, not sub
🔁 Summary
| Item | Meaning |
|---|---|
__init__.py | Makes folder a package |
| Can be empty | Yes |
| Can have code | Yes (runs on import) |
| Can control what to import | Yes with __all__ |
📝 Practice Task
❓ Create a package with:
__init__.py(prints “Package loaded”)calc.py(function to add numbers)- Then import and use it.
✅ Answer:
Folder: tools/
➡️ __init__.py
print("Package loaded!")
➡️ calc.py
def add(a, b):
return a + b
➡️ Main file:
from tools import calc
print(calc.add(4, 5)) # Output: 9
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