068-init-module.md

The __init__ Module

We can subpackage modules by simple creating a folder with Python files next to the script we are running (usually main.py). In this case we add a folder called mylib with a file called mymod.py:

# mylib/mymod.py
def main_func(message):
    print(message)

Which allows us to import it in the main script using dot notation:

# main.py
from mylib.mymod import main_func

main_func("https://ariel.ninja")

# What are these objects?
import mylib
from mylib import mymod
print(mylib) # <module 'mylib' (<_frozen_importlib_external.NamespaceLoader object ...>)>
print(mymod) # <module 'mylib.mymod' from 'mylib/mymod.py'>

Those print statements at the end hint to our next step. mylib is the "package" that includes all the submodules. And mymod is a module object. But in fact mylib could be its own module, the top-level module of the package by containing an __init__.py file. If so, that is what gets imported when importing a library or package:

# mylib/__init__.py
from .mymod import main_func

Notice how we can use relative paths by starting with a period like from .mymod import .... Now we can use this init module by importing the package directly:

# main.py
from mylib import main_func
main_func("Hire me!")

import mylib as ml
assert ml.__file__.endswith("__init__.py")

print(ml)  # <module 'mylib.mymod' from 'mylib/__init__.py'>