When you run a command that imports a package (like from geometry.shapes import ...), Python executes the code inside that package's __init__.py file once and only once during that session.
Here is exactly what happens when it runs:
1. The Execution Trigger
The moment any part of the package is touched for the first time, Python runs the __init__.py file.
- If you run
import geometry, it runs. - If you run
from geometry.shapes import circle_area, it also runs before it even looks atshapes.py.
2. Namespace Creation
Everything defined in __init__.py (variables, functions, classes) becomes an attribute of the package object.
Example:
If you change your geometry/__init__.py to look like this:
print("Initializing the Geometry package!")
VERSION = "1.0.0"Then when you run your script, you will see "Initializing the Geometry package!" printed in the terminal, and you could access geometry.VERSION in your main script.
3. Sub-module Management
If your package has many modules, you can use __init__.py to pre-load them. This is often used to "expose" functions so the user doesn't have to know the exact file structure.
For example, if you put this in geometry/__init__.py:
from .shapes import circle_areaThe user can then call geometry.circle_area() directly, without needing to type geometry.shapes.circle_area().
Summary
Think of __init__.py as a "Welcome Mat" or a "Setup Script". It prepares the environment for the rest of your package to work correctly, ensuring that any necessary settings or shortcuts are ready before you start using the actual logic in files like shapes.py.
