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I have read the documentation and there is something I'm still not sure about. Does all the initialisation code for the whole module in __init__.py get run if I do:
from mymodule import mything
or only if I do
import mymodule
What gets run from __init__.py and when does it get run?
I'm sure I could also test this fairly easy, but for posterity and helpfulness for others, I thought I'd ask here.
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The __init__.py file makes Python treat directories containing it as modules. Furthermore, this is the first file to be loaded in a module, so you can use it to execute code that you want to run each time a module is loaded, or specify the submodules to be exported.
Leaving an __init__.py file empty is considered normal and even a good practice, if the package's modules and sub-packages do not need to share any code.
So it's normally a good place to put any package-level initialisation code. The bottom line is: all names assigned in __init__.py , be it imported modules, functions or classes, are automatically available in the package namespace whenever you import the package or a module in the package.
If you have setup.py in your project and you use find_packages() within it, it is necessary to have an __init__.py file in every directory for packages to be automatically found.
The code in __init__.py is run whenever you import anything from the package. That includes importing other modules in that package.
The style of import (import packagename or from packagename import some_name) doesn't matter here.
Like all modules, the code is run just once, and entered into sys.modules under the package name.
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